http://journals.iucr.org/a/journalhomepage.html Acta Crystallographica Section A: Foundations of Crystallography publishes papers reporting fundamental advances in all areas of crystallography in the broadest sense. The central themes are, on the one hand, experimental and theoretical studies of the properties and arrangements of atoms, ions and molecules in condensed matter, ideal or real, and of their symmetry and, on the other, the theoretical and experimental aspects of the various methods to determine these arrangements. en-gb Copyright (c) 2009 International Union of Crystallography International Union of Crystallography International Union of Crystallography http://journals.iucr.org urn:issn:0567-7394 Acta Crystallographica Section A: Foundations of Crystallography publishes papers reporting fundamental advances in all areas of crystallography in the broadest sense. The central themes are, on the one hand, experimental and theoretical studies of the properties and arrangements of atoms, ions and molecules in condensed matter, ideal or real, and of their symmetry and, on the other, the theoretical and experimental aspects of the various methods to determine these arrangements. text/html Open access article in Acta Crystallographica Section A Foundations of Crystallography text yearly 6 2002-01-01T00:00+00:00 med@iucr.org Acta Crystallographica Section A Foundations of Crystallography Copyright (c) 2009 International Union of Crystallography urn:issn:0567-7394 http://journals.iucr.org/logos/rss10a.gif http://journals.iucr.org/a/journalhomepage.html Still image http://scripts.iucr.org/cgi-bin/paper?sh5087 In the 60 years since its birth in 1948, the number of journals published by the International Union of Crystallography has risen from one to eight. A brief account of the history of the forerunner of the IUCr journals, Zeitschrift für Kristallographie, is given. The context of the birth of the IUCr and the first of its journals, Acta Crystallographica, is recalled. The circumstances which led to the growth of Acta into several sections, at first A and B then, successively, C, D, E and F, and the launch of two new journals, the Journal of Applied Crystallography and the Journal of Synchrotron Radiation, are described. The transition from print-on-paper to electronic journals is also remembered. Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7673 Authier, A. 2009-05-01 doi:10.1107/S0108767309007235 International Union of Crystallography The birth and growth of the publications and journals of the International Union of Crystallography from 1948 to 2008 are described. Details are given of the pre-war history that led up to their creation and development. en PUBLISHING; ACTA CRYSTALLOGRAPHICA; JOURNAL OF APPLIED CRYSTALLOGRAPHY; JOURNAL OF SYNCHROTRON RADIATION; INTERNATIONAL TABLES FOR CRYSTALLOGRAPHY; INTERNATIONAL UNION OF CRYSTALLOGRAPHY In the 60 years since its birth in 1948, the number of journals published by the International Union of Crystallography has risen from one to eight. A brief account of the history of the forerunner of the IUCr journals, Zeitschrift für Kristallographie, is given. The context of the birth of the IUCr and the first of its journals, Acta Crystallographica, is recalled. The circumstances which led to the growth of Acta into several sections, at first A and B then, successively, C, D, E and F, and the launch of two new journals, the Journal of Applied Crystallography and the Journal of Synchrotron Radiation, are described. The transition from print-on-paper to electronic journals is also remembered. text/html 60 years of IUCr journals text 3 65 2009-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2009 International Union of Crystallography 0108-7673 feature articles 167 med@iucr.org 182 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0070 Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7673 Nespolo, M. 2009-03-01 doi:10.1107/S0108767309002013 International Union of Crystallography en BOOK REVIEW text/html Crystallography and the World of Symmetry. By Sanat K. Chatterjee. Springer Series in Materials Sciences, No. 113. Springer, 2008. Pp. xi + 150. Price (hardback) GBP 87.00. ISBN 978-3-540-69898-2. text 2 65 2009-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2009 International Union of Crystallography 0108-7673 book reviews 164 med@iucr.org 166 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh5079 We present a method for geometric construction of periodic three-dimensional Euclidean nets by projecting two-dimensional hyperbolic tilings onto a family of triply periodic minimal surfaces (TPMSs). Our techniques extend the combinatorial tiling theory of Dress, Huson & Delgado-Friedrichs to enumerate simple reticulations of these TPMSs. We include a taxonomy of all networks arising from kaleidoscopic hyperbolic tilings with up to two distinct tile types (and their duals, with two distinct vertices), mapped to three related TPMSs, namely Schwarz's primitive (P) and diamond (D) surfaces, and Schoen's gyroid (G). Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7673 Ramsden, S.J. Robins, V. Hyde, S.T. 2009-03-01 doi:10.1107/S0108767308040592 International Union of Crystallography Systematic enumeration of tilings of the two-dimensional hyperbolic plane leads to ab initio construction of triply periodic nets via projection of the tilings onto triply periodic minimal surfaces. The technique is described in detail for kaleidoscopic tilings, projected onto the P, D and G (gyroid) minimal surfaces. en THREE-DIMENSIONAL EUCLIDEAN NETS; TWO-DIMENSIONAL HYPERBOLIC TILINGS; TRIPLY PERIODIC MINIMAL SURFACES; KALEIDOSCOPIC HYPERBOLIC TILINGS We present a method for geometric construction of periodic three-dimensional Euclidean nets by projecting two-dimensional hyperbolic tilings onto a family of triply periodic minimal surfaces (TPMSs). Our techniques extend the combinatorial tiling theory of Dress, Huson & Delgado-Friedrichs to enumerate simple reticulations of these TPMSs. We include a taxonomy of all networks arising from kaleidoscopic hyperbolic tilings with up to two distinct tile types (and their duals, with two distinct vertices), mapped to three related TPMSs, namely Schwarz's primitive (P) and diamond (D) surfaces, and Schoen's gyroid (G). text/html Three-dimensional Euclidean nets from two-dimensional hyperbolic tilings: kaleidoscopic examples text 2 65 2009-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2009 International Union of Crystallography 0108-7673 lead articles 81 med@iucr.org 108 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0068 Copyright (c) 2009 International Union of Crystallography urn:issn:0108-7673 Garnier, E. 2009-01-01 doi:10.1107/S010876730802850X International Union of Crystallography en BOOK REVIEW text/html Powder Diffraction. Theory and Practice. Edited by R. E. Dinnebier and S. J. L. Billinge. Cambridge: RSC Publishing, 2008. Pp. xxi + 582. Price (hardcover): GBP 59.00. ISBN (online): 978-1-84755-823-7; ISBN (print): 978-0-85404-231-9. text 1 65 2009-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2009 International Union of Crystallography 0108-7673 book reviews 51 med@iucr.org 51 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0065 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Müller, U. 2008-07-01 doi:10.1107/S0108767308017042 International Union of Crystallography en BOOK REVIEW text/html Advanced structural inorganic chemistry. IUCr Texts on Crystallography No. 10. By Wai-Kee Li, Gong-Du Zhou and Thomas Chung Wai Mak. Oxford: Oxford University Press, 2008. Pp. xx + 819. Price (paperback) GBP 37.50. ISBN 978-0-19-921695-6. text 4 64 2008-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 book reviews 513 med@iucr.org 514 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0060 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Schreiber, M. 2008-05-01 doi:10.1107/S0108767308009343 International Union of Crystallography en BOOK REVIEW text/html Aperiodic crystals: from modulated phases to quasicrystals. By T. Janssen, G. Chapuis, and M. de Boissieu. IUCr Monographs on Crystallography, No. 20. Oxford: IUCr/Oxford University Press, 2007. Pp. 466. Price GBP 75.00. ISBN 978-0-19-856777-6. text 3 64 2008-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 book reviews 433 med@iucr.org 434 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0054 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Reich, K. 2008-05-01 doi:10.1107/S0108767308006880 International Union of Crystallography en BOOK REVIEW text/html Out of the shadows. Contributions of twentieth-century women to physics. Edited by Nina Byers and Gary Williams. Cambridge: Cambridge University Press, 2006. Pp. xxv + 471. Price (hardback) GBP 30.00. ISBN-13 978-0-521-82197-1. text 3 64 2008-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 book reviews 432 med@iucr.org 432 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0058 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Dodson, G. 2008-03-01 doi:10.1107/S0108767308002407 International Union of Crystallography en BOOK REVIEW text/html J. D. Bernal. The sage of science. By Andrew Brown. Pp. 576. Oxford: Oxford University Press, 2007. Price (paperback) GBP 12.99. ISBN 978-0-19-920565-3 text 2 64 2008-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 book reviews 349 med@iucr.org 351 1600-5724 http://scripts.iucr.org/cgi-bin/paper?es0363 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 2008-03-01 doi:10.1107/S0108767308002572 International Union of Crystallography en EWALD PRIZE text/html Ewald Prize Award text 2 64 2008-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 international union of crystallography 352 med@iucr.org 352 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0039 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 2008-05-01 doi:10.1107/S0108767308002432 International Union of Crystallography en BOOK RECEIVED text/html Inorganic structural chemistry. By Ulrich Müller. Pp. xi + 268. Chichester: John Wiley & Sons, 2nd ed., 2006. Price (soft cover) GBP 29.95. ISBN 978-0-470-01864-4. text 3 64 2008-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 books received 435 med@iucr.org 435 1600-5724 http://scripts.iucr.org/cgi-bin/paper?me0360 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Schenk, H. 2008-01-01 doi:10.1107/S0108767307067098 International Union of Crystallography en PREFACE text/html Crystallography Across the Sciences 2 text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 issue preface med@iucr.org http://scripts.iucr.org/cgi-bin/paper?sc5024 This paper discusses the trends in the experimental studies of molecular organic solids at high pressures by diffraction techniques. Crystallization of liquids, crystallization from solutions and solid-state transformations are considered. Special attention is paid to the high-pressure studies of pharmaceuticals and of biomimetics. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Boldyreva, E.V. 2008-01-01 doi:10.1107/S0108767307065786 International Union of Crystallography A concise review of the retrospect and prospects of high-pressure diffraction studies of organic crystals, with a special emphasis on pharmaceuticals and biomimetics. en COMPRESSIBILITY; HYDROGEN BONDS; HYDROSTATIC PRESSURES; KINETIC CONTROL; LATTICE STRAIN; PHASE TRANSITIONS; POLYMORPHISM; SOLVENT-MEDIATED TRANSFORMATIONS This paper discusses the trends in the experimental studies of molecular organic solids at high pressures by diffraction techniques. Crystallization of liquids, crystallization from solutions and solid-state transformations are considered. Special attention is paid to the high-pressure studies of pharmaceuticals and of biomimetics. text/html High-pressure diffraction studies of molecular organic solids. A personal view text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 218 med@iucr.org 231 http://scripts.iucr.org/cgi-bin/paper?sc5018 Structural studies of materials with nano-sized spaces, called nano-structured materials, have been carried out by high-resolution powder diffraction. Our developed analytical method, which is the combination of the maximum-entropy method (MEM) and Rietveld refinement, the so-called MEM/Rietveld method, has been successfully applied to the analysis of synchrotron-radiation (SR) powder diffraction data measured at SPring-8, a third-generation SR light source. In this article, structural studies of nano-porous coordination polymers and endohedral metallofullerenes are presented with the advanced technique of SR powder experiment. The structure of the adsorbed guest molecule in the coordination polymer and encapsulated atoms in the fullerene cage are clearly revealed by the MEM charge density. The methodology of MEM/Rietveld analysis is also presented. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Takata, M. 2008-01-01 doi:10.1107/S010876730706521X International Union of Crystallography The role played by the MEM/Rietveld method, which is a combination of the maximum-entropy method (MEM) and Rietveld analysis, for charge-density studies is described in the structural materials science of novel nano-materials. The atoms' and molecules' charge densities inside the nano-scale spaces of fullerene cages and metal-organic coordination polymers are visualized by using synchrotron-radiation powder data. en CHARGE DENSITY; MAXIMUM-ENTROPY METHOD; METALLOFULLERENE; NANO-MATERIAL; POROUS COORDINATION POLYMERS; POWDER DIFFRACTION; SYNCHROTRON RADIATION Structural studies of materials with nano-sized spaces, called nano-structured materials, have been carried out by high-resolution powder diffraction. Our developed analytical method, which is the combination of the maximum-entropy method (MEM) and Rietveld refinement, the so-called MEM/Rietveld method, has been successfully applied to the analysis of synchrotron-radiation (SR) powder diffraction data measured at SPring-8, a third-generation SR light source. In this article, structural studies of nano-porous coordination polymers and endohedral metallofullerenes are presented with the advanced technique of SR powder experiment. The structure of the adsorbed guest molecule in the coordination polymer and encapsulated atoms in the fullerene cage are clearly revealed by the MEM charge density. The methodology of MEM/Rietveld analysis is also presented. text/html The MEM/Rietveld method with nano-applications – accurate charge-density studies of nano-structured materials by synchrotron-radiation powder diffraction text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 232 med@iucr.org 245 http://scripts.iucr.org/cgi-bin/paper?sc5021 This review describes the development and application of a new crystallographic technique that is starting to enable the three-dimensional structural determination of molecules in their photo-activated states. So called `photocrystallog­raphy' has wide applicability, particularly in the currently exciting area of photonics, and a discussion of this applied potential is put into context in this article. Studies are classified into four groups: photo-structural changes that are (i) irreversible; (ii) long-lived but reversible under certain conditions; (iii) transient with photo-active lifetimes of the order of microseconds; (iv) very short lived, existing at the nanosecond or even picosecond level. As photo-structural changes relative to the `ground state' can be subtle, this article necessarily concentrates on small-molecule single-crystal X-ray diffraction given that high atomic resolution is possible. That said, where it is pertinent, references are also made to related major advances in photo-induced macromolecular crystallography. The review concludes with an outlook on this new research area, including the future possibility of studying even more ephemeral, femtosecond-lived, photo-active species. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Cole, J.M. 2008-01-01 doi:10.1107/S0108767307065324 International Union of Crystallography A review of crystal-structure determinations of photo-induced molecular species, as derived using small-molecule single-crystal X-ray crystallography, is presented. Such species may be stable or transient, down to picoseconds, and are of substantial interest to the photonics industry. en PHOTOCRYSTALLOGRAPHY This review describes the development and application of a new crystallographic technique that is starting to enable the three-dimensional structural determination of molecules in their photo-activated states. So called `photocrystallog­raphy' has wide applicability, particularly in the currently exciting area of photonics, and a discussion of this applied potential is put into context in this article. Studies are classified into four groups: photo-structural changes that are (i) irreversible; (ii) long-lived but reversible under certain conditions; (iii) transient with photo-active lifetimes of the order of microseconds; (iv) very short lived, existing at the nanosecond or even picosecond level. As photo-structural changes relative to the `ground state' can be subtle, this article necessarily concentrates on small-molecule single-crystal X-ray diffraction given that high atomic resolution is possible. That said, where it is pertinent, references are also made to related major advances in photo-induced macromolecular crystallography. The review concludes with an outlook on this new research area, including the future possibility of studying even more ephemeral, femtosecond-lived, photo-active species. text/html Photocrystallography text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 259 med@iucr.org 271 http://scripts.iucr.org/cgi-bin/paper?sc5019 Advances made over the past decade in structure determination from powder diffraction data are reviewed with particular emphasis on algorithmic developments and the successes and limitations of the technique. While global optimization methods have been successful in the solution of molecular crystal structures, new methods are required to make the solution of inorganic crystal structures more routine. The use of complementary techniques such as NMR to assist structure solution is discussed and the potential for the combined use of X-ray and neutron diffraction data for structure verification is explored. Structures that have proved difficult to solve from powder diffraction data are reviewed and the limitations of structure determination from powder diffraction data are discussed. Furthermore, the prospects of solving small protein crystal structures over the next decade are assessed. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 David, W.I.F. Shankland, K. 2008-01-01 doi:10.1107/S0108767307064252 International Union of Crystallography Structure determination from powder diffraction data has developed in the past decade to the stage where the structures of many molecular materials, particularly of pharmaceutical interest, are successfully solved. The intrinsically higher symmetry and more complex topology of inorganic materials complicate their structure determination from powder diffraction data which is, as a result, less routine than its molecular counterpart. The study of small proteins from powder diffraction data alone shows great promise and the first structures have been solved. The limits of the powder diffraction technique remain to be explored, particularly if auxiliary techniques are used. en GLOBAL OPTIMIZATION; DIRECT METHODS; POWDER DIFFRACTION; STRUCTURE DETERMINATION Advances made over the past decade in structure determination from powder diffraction data are reviewed with particular emphasis on algorithmic developments and the successes and limitations of the technique. While global optimization methods have been successful in the solution of molecular crystal structures, new methods are required to make the solution of inorganic crystal structures more routine. The use of complementary techniques such as NMR to assist structure solution is discussed and the potential for the combined use of X-ray and neutron diffraction data for structure verification is explored. Structures that have proved difficult to solve from powder diffraction data are reviewed and the limitations of structure determination from powder diffraction data are discussed. Furthermore, the prospects of solving small protein crystal structures over the next decade are assessed. text/html Structure determination from powder diffraction data text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 52 med@iucr.org 64 http://scripts.iucr.org/cgi-bin/paper?sc5020 A large number of polished stone implements from Palaeolithic to Bronze Age sites of Northern Italy and Southern France are made of high-pressure (HP) metamorphic rocks (eclogite and related rocks), mainly consisting of Na-pyroxene (jadeite to omphacite) from the metamorphic belt of the Western Alps. The standard archaeometric study of prehistoric stone implements follows a procedure that is invasive, expensive and time-consuming. Since Na-pyroxenes may show a large compositional range, a thorough study of the variations affecting the dhkl values, obtained by X-ray diffraction, of three selected reflections as a function of different chemical composition was carried out, in order to determine the chemistry of Na-pyroxene isomorphic mixtures and roughly evaluate their relative amounts. These reflections (\bar221, 310, 002) are sharp, intense and sensitive to the variation of pyroxene chemical composition. Using such dhkl values measured on pyroxenes of known chem­istry, a Ca-pyroxene(Di)–jadeite(Jd)–aegirine(Ae) compositional diagram was constructed, from which the composition of an unknown pyroxene can be estimated within an error of about 5%. When the size of the object is relatively small and a flat polished surface is present, the proposed analytical procedure becomes totally non-invasive. The data obtained shed light on the provenance sources of such implements and the prehistoric trade routes. urn:issn:0108-7673 Giustetto, R. Chiari, G. Compagnoni, R. 2008-01-01 doi:10.1107/S0108767307062691 International Union of Crystallography An innovative non-destructive method is presented for determining the chemistry of Na-pyroxene isomorphic mixtures characterizing Neolithic greenstone implements which permits their provenance and some of the prehistoric trade routes to be traced. en CLINOPYROXENE; COMPOSITIONAL GRID; JADEITE; NEOLITHIC GREENSTONE IMPLEMENTS; OMPHACITE A large number of polished stone implements from Palaeolithic to Bronze Age sites of Northern Italy and Southern France are made of high-pressure (HP) metamorphic rocks (eclogite and related rocks), mainly consisting of Na-pyroxene (jadeite to omphacite) from the metamorphic belt of the Western Alps. The standard archaeometric study of prehistoric stone implements follows a procedure that is invasive, expensive and time-consuming. Since Na-pyroxenes may show a large compositional range, a thorough study of the variations affecting the dhkl values, obtained by X-ray diffraction, of three selected reflections as a function of different chemical composition was carried out, in order to determine the chemistry of Na-pyroxene isomorphic mixtures and roughly evaluate their relative amounts. These reflections (\bar221, 310, 002) are sharp, intense and sensitive to the variation of pyroxene chemical composition. Using such dhkl values measured on pyroxenes of known chem­istry, a Ca-pyroxene(Di)–jadeite(Jd)–aegirine(Ae) compositional diagram was constructed, from which the composition of an unknown pyroxene can be estimated within an error of about 5%. When the size of the object is relatively small and a flat polished surface is present, the proposed analytical procedure becomes totally non-invasive. The data obtained shed light on the provenance sources of such implements and the prehistoric trade routes. text/html An easy non-invasive X-ray diffraction method to determine the composition of Na-pyroxenes from high-density `greenstone' implements text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography 0108-7673 feature articles 161 med@iucr.org 168 http://scripts.iucr.org/cgi-bin/paper?sc5016 Since the late 1950's, high-pressure structural studies have become increasingly frequent, following the inception of opposed-anvil cells, development of efficient diffractometric equipment (brighter radiation sources both in laboratories and in synchrotron facilities, highly efficient area detectors) and procedures (for crystal mounting, centring, pressure calibration, collecting and correcting data). Consequently, during the last decades, high-pressure crystallography has evolved into a powerful technique which can be routinely applied in laboratories and dedicated synchrotron and neutron facilities. The variation of pressure adds a new thermodynamic dimension to crystal-structure analyses, and extends the understanding of the solid state and materials in general. New areas of thermodynamic exploration of phase diagrams, polymorphism, transformations between different phases and cohesion forces, structure–property relations, and a deeper understanding of matter at the atomic scale in general are accessible with the high-pressure techniques in hand. A brief history, guidelines and requirements for performing high-pressure structural studies are outlined. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Katrusiak, A. 2008-01-01 doi:10.1107/S0108767307061181 International Union of Crystallography The history and development of high-pressure crystallography are briefly described and examples of structural transformations in compressed compounds are given. The review is focused on the diamond-anvil cell, celebrating its 50th anniversary this year, the principles of its operation and the impact it has had on high-pressure X-ray diffraction. en DIFFRACTION; HIGH PRESSURE; HYDROGEN BONDS; PHASE TRANSITIONS; POLYMORPHISM; THERMODYNAMICS Since the late 1950's, high-pressure structural studies have become increasingly frequent, following the inception of opposed-anvil cells, development of efficient diffractometric equipment (brighter radiation sources both in laboratories and in synchrotron facilities, highly efficient area detectors) and procedures (for crystal mounting, centring, pressure calibration, collecting and correcting data). Consequently, during the last decades, high-pressure crystallography has evolved into a powerful technique which can be routinely applied in laboratories and dedicated synchrotron and neutron facilities. The variation of pressure adds a new thermodynamic dimension to crystal-structure analyses, and extends the understanding of the solid state and materials in general. New areas of thermodynamic exploration of phase diagrams, polymorphism, transformations between different phases and cohesion forces, structure–property relations, and a deeper understanding of matter at the atomic scale in general are accessible with the high-pressure techniques in hand. A brief history, guidelines and requirements for performing high-pressure structural studies are outlined. text/html High-pressure crystallography text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 135 med@iucr.org 148 http://scripts.iucr.org/cgi-bin/paper?sc5017 The study of crystals at atomic level by electrons – electron crystallography – is an important complement to X-ray crystallography. There are two main advantages of structure determinations by electron crystallography compared to X-ray diffraction: (i) crystals millions of times smaller than those needed for X-ray diffraction can be studied and (ii) the phases of the crystallographic structure factors, which are lost in X-ray diffraction, are present in transmission-electron-microscopy (TEM) images. In this paper, some recent developments of electron crystallography and its applications, mainly on inorganic crystals, are shown. Crystal structures can be solved to atomic resolution in two dimensions as well as in three dimensions from both TEM images and electron diffraction. Different techniques developed for electron crystallography, including three-dimensional reconstruction, the electron precession technique and ultrafast electron crystallography, are reviewed. Examples of electron-crystallography applications are given. There is in principle no limitation to the complexity of the structures that can be solved by electron crystallography. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Zou, X.D. Hovmöller, S. 2008-01-01 doi:10.1107/S0108767307060084 International Union of Crystallography Different techniques for structure determination from transmission electron microscopy and electron diffraction are reviewed, including three-dimensional reconstruction, the precession technique and ultrafast electron crystallography. Examples of electron-crystallography applications are given. en ELECTRON CRYSTALLOGRAPHY; ELECTRON PRECESSION TECHNIQUE; THREE-DIMENSIONAL RECONSTRUCTION; ULTRAFAST ELECTRON CRYSTALLOGRAPHY The study of crystals at atomic level by electrons – electron crystallography – is an important complement to X-ray crystallography. There are two main advantages of structure determinations by electron crystallography compared to X-ray diffraction: (i) crystals millions of times smaller than those needed for X-ray diffraction can be studied and (ii) the phases of the crystallographic structure factors, which are lost in X-ray diffraction, are present in transmission-electron-microscopy (TEM) images. In this paper, some recent developments of electron crystallography and its applications, mainly on inorganic crystals, are shown. Crystal structures can be solved to atomic resolution in two dimensions as well as in three dimensions from both TEM images and electron diffraction. Different techniques developed for electron crystallography, including three-dimensional reconstruction, the electron precession technique and ultrafast electron crystallography, are reviewed. Examples of electron-crystallography applications are given. There is in principle no limitation to the complexity of the structures that can be solved by electron crystallography. text/html Electron crystallography: imaging and single-crystal diffraction from powders text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 149 med@iucr.org 160 http://scripts.iucr.org/cgi-bin/paper?sc5023 In the paper by Sayre [Acta Cryst. (2008), A64, 33–35], a proposal is made to use stereoscopy as a short-term means of overcoming the primarily technological hurdles involved in three-dimensional imaging of the biological cell by soft X-ray diffraction microscopy. This addendum provides a broader perspective on the techniques used by this rapidly maturing community to investigate structural problems in the biological and material sciences. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Shapiro, D.A. 2008-01-01 doi:10.1107/S0108767307057571 International Union of Crystallography A broad perspective on the techniques used by the coherent X-ray diffraction microscopy community is provided as an addendum to the paper by Sayre [Acta Cryst. (2008), A64, 33–35]. en YEAST CELL; THREE-DIMENSIONAL IMAGING; FLASH IMAGING; SERIAL CRYSTALLOGRAPHY In the paper by Sayre [Acta Cryst. (2008), A64, 33–35], a proposal is made to use stereoscopy as a short-term means of overcoming the primarily technological hurdles involved in three-dimensional imaging of the biological cell by soft X-ray diffraction microscopy. This addendum provides a broader perspective on the techniques used by this rapidly maturing community to investigate structural problems in the biological and material sciences. text/html Report on a project on three-dimensional imaging of the biological cell by single-particle X-ray diffraction. Addendum text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 36 med@iucr.org 37 http://scripts.iucr.org/cgi-bin/paper?sc5022 Single-particle X-ray diffraction is an extension of X-ray crystallography which allows the specimen to be any small solid-state bounded object; in Shapiro et al. [Proc. Natl Acad. Sci. USA (2005), 102, 15343–15346] and Thibault et al. [Acta Cryst. (2006), A62, 248–261], the reader can find descriptions of a recent StonyBrook/Berkeley/Cornell two-dimensional imaging of a yeast cell by this technique. Our present work is aimed at extending the technique to the three-dimensional imaging of a cell. However, the usual method of doing that, namely rotating the specimen into many orientations in the X-ray beam, has not as yet given sufficiently good three-dimensional diffraction data to allow the work to go forward, the largest problem being the difficulty of preventing unwanted levels of change in the specimen through the extended exposure to a hostile environment of X-rays and, in some cases, high vacuum and/or extreme cold. The present paper discusses possible methods of dealing with this problem. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Sayre, D. 2008-01-01 doi:10.1107/S010876730705550X International Union of Crystallography In biocellular imaging, unwanted changes in the specimen during the longer exposures for three-dimensional data collection are making the step from two- to three-dimensional imaging difficult. Low-exposure stereoscopic three-dimensional imaging may be one answer to the problem. en YEAST CELL; THREE-DIMENSIONAL IMAGING; STEREOSCOPIC IMAGING Single-particle X-ray diffraction is an extension of X-ray crystallography which allows the specimen to be any small solid-state bounded object; in Shapiro et al. [Proc. Natl Acad. Sci. USA (2005), 102, 15343–15346] and Thibault et al. [Acta Cryst. (2006), A62, 248–261], the reader can find descriptions of a recent StonyBrook/Berkeley/Cornell two-dimensional imaging of a yeast cell by this technique. Our present work is aimed at extending the technique to the three-dimensional imaging of a cell. However, the usual method of doing that, namely rotating the specimen into many orientations in the X-ray beam, has not as yet given sufficiently good three-dimensional diffraction data to allow the work to go forward, the largest problem being the difficulty of preventing unwanted levels of change in the specimen through the extended exposure to a hostile environment of X-rays and, in some cases, high vacuum and/or extreme cold. The present paper discusses possible methods of dealing with this problem. text/html Report on a project on three-dimensional imaging of the biological cell by single-particle X-ray diffraction text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 33 med@iucr.org 35 http://scripts.iucr.org/cgi-bin/paper?sc5013 The morphotropic phase boundary in the phase diagram of the technologically important Pb(ZrxTi1−x)O3 (PZT) ceramics has been traditionally believed to separate ferroelectric tetragonal and rhombohedral phase regions. This old picture has come under close scrutiny during the last eight years following the discovery of new monoclinic phases in the Cm and Cc space groups. This article presents a brief overview of these discoveries in which the use of multiple diffraction probes (X-ray, electron, neutron diffraction) in conjunction with physical property measurements has played a crucial role. A new phase diagram of PZT showing the stability fields of these structures below room temperature is also presented. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Pandey, D. Singh, A.K. Baik, S. 2008-01-01 doi:10.1107/S0108767307055511 International Union of Crystallography An overview of the recent discoveries of the monoclinic phases in the Cm and Cc space groups and their stability fields in the Pb(ZrxTi1−x)O3 phase diagram is presented. en FERROIC PHASES; PIEZOELECTRIC PB(ZRXTI1-X)O3 CERAMICS (PZT) The morphotropic phase boundary in the phase diagram of the technologically important Pb(ZrxTi1−x)O3 (PZT) ceramics has been traditionally believed to separate ferroelectric tetragonal and rhombohedral phase regions. This old picture has come under close scrutiny during the last eight years following the discovery of new monoclinic phases in the Cm and Cc space groups. This article presents a brief overview of these discoveries in which the use of multiple diffraction probes (X-ray, electron, neutron diffraction) in conjunction with physical property measurements has played a crucial role. A new phase diagram of PZT showing the stability fields of these structures below room temperature is also presented. text/html Stability of ferroic phases in the highly piezoelectric Pb(ZrxTi1−x)O3 ceramics text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 192 med@iucr.org 203 http://scripts.iucr.org/cgi-bin/paper?pf0061 Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Rutherford, J.S. 2008-03-01 doi:10.1107/S0108767308002419 International Union of Crystallography en BOOK REVIEW text/html Theories and techniques of crystal structure determination. By Uri Shmueli, Pp. 269. Oxford: Oxford University Press, 2007. Price GBP 32.50. ISBN 978-0-19-921350-4. text 2 64 2008-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 book reviews 348 med@iucr.org 348 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sc5014 The 2003 outbreak of severe acute respiratory syndrome (SARS), caused by a previously unknown coronavirus called SARS-CoV, had profound social and economic impacts worldwide. Since then, structure–function studies of SARS-CoV proteins have provided a wealth of information that increases our understanding of the underlying mechanisms of SARS. While no effective therapy is currently available, considerable efforts have been made to develop vaccines and drugs to prevent SARS-CoV infection. In this review, some of the notable achievements made by SARS structural biology projects worldwide are examined and strategies for therapeutic intervention are discussed based on available SARS-CoV protein structures. To date, 12 structures have been determined by X-ray crystallography or NMR from the 28 proteins encoded by SARS-CoV. One key protein, the SARS-CoV main protease (Mpro), has been the focus of considerable structure-based drug discovery efforts. This article highlights the importance of structural biology and shows that structures for drug design can be rapidly determined in the event of an emerging infectious disease. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Bartlam, M. Xue, X. Rao, Z. 2008-01-01 doi:10.1107/S0108767307054426 International Union of Crystallography The severe acute respiratory syndrome (SARS) coronavirus outbreak in 2003 had profound social and economic impacts worldwide. This review highlights the importance of structural biology and shows that structures for drug design can be rapidly determined in the event of an emerging infectious disease. en DRUG DESIGN; SARS CORONAVIRUS; SARS-COV The 2003 outbreak of severe acute respiratory syndrome (SARS), caused by a previously unknown coronavirus called SARS-CoV, had profound social and economic impacts worldwide. Since then, structure–function studies of SARS-CoV proteins have provided a wealth of information that increases our understanding of the underlying mechanisms of SARS. While no effective therapy is currently available, considerable efforts have been made to develop vaccines and drugs to prevent SARS-CoV infection. In this review, some of the notable achievements made by SARS structural biology projects worldwide are examined and strategies for therapeutic intervention are discussed based on available SARS-CoV protein structures. To date, 12 structures have been determined by X-ray crystallography or NMR from the 28 proteins encoded by SARS-CoV. One key protein, the SARS-CoV main protease (Mpro), has been the focus of considerable structure-based drug discovery efforts. This article highlights the importance of structural biology and shows that structures for drug design can be rapidly determined in the event of an emerging infectious disease. text/html The search for a structural basis for therapeutic intervention against the SARS coronavirus text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 204 med@iucr.org 213 http://scripts.iucr.org/cgi-bin/paper?sc5012 As the first centennial of X-ray diffraction is inevitably drawing closer, it is tempting to reflect on the impact that this fascinating discipline has had on natural sciences and how it has changed the world we live in. Also, next year is the 160th anniversary of the fateful April afternoon when Louis Pasteur separated d- from l-tartrate crystals, an event that many science historians recognize as the birth of stereochemistry, and the first step that the barely nascent field of crystallography took on the road to elucidate a fundamental phenomenon of chemistry and biology – chirality. Many great minds – Pasteur, Van 't Hoff, Fischer, Lord Kelvin, the Braggs, Astbury and Bijvoet, to mention just a few – contributed along the way. But one central inanimate character was there at all times – an inconspicuous somewhat obscure organic compound found in wine: tartaric acid. This is the story of its contribution to science. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Derewenda, Z.S. 2008-01-01 doi:10.1107/S0108767307054293 International Union of Crystallography How tartaric acid, an inconspicuous organic compound found in wine, made a pivotal contribution to structural chemistry and biology. en CHIRALITY; TARTARIC ACID As the first centennial of X-ray diffraction is inevitably drawing closer, it is tempting to reflect on the impact that this fascinating discipline has had on natural sciences and how it has changed the world we live in. Also, next year is the 160th anniversary of the fateful April afternoon when Louis Pasteur separated d- from l-tartrate crystals, an event that many science historians recognize as the birth of stereochemistry, and the first step that the barely nascent field of crystallography took on the road to elucidate a fundamental phenomenon of chemistry and biology – chirality. Many great minds – Pasteur, Van 't Hoff, Fischer, Lord Kelvin, the Braggs, Astbury and Bijvoet, to mention just a few – contributed along the way. But one central inanimate character was there at all times – an inconspicuous somewhat obscure organic compound found in wine: tartaric acid. This is the story of its contribution to science. text/html On wine, chirality and crystallography text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 246 med@iucr.org 258 http://scripts.iucr.org/cgi-bin/paper?sc5015 The history of crystallographic computing and use of crystallographic software is one which traces the escape from the drudgery of manual human calculations to a world where the user delegates most of the travail to electronic computers. In practice, this involves practising crystallographers communicating their thoughts to the crystallographic program authors, in the hope that new procedures will be implemented within their software. Against this background, the development of small-molecule single-crystal and powder diffraction software is traced. Starting with the analogue machines and the use of Hollerith tabulators of the late 1930's, it is shown that computing developments have been science led, with new technologies being harnessed to solve pressing crystallographic problems. The development of software is also traced, with a final caution that few of the computations now performed daily are really understood by the program users. Unless a sufficient body of people continues to dismantle and re-build programs, the knowledge encoded in the old programs will become as inaccessible as the knowledge of how to build the Great Pyramid at Giza. urn:issn:0108-7673 Cranswick, L.M.D. 2008-01-01 doi:10.1107/S0108767307051355 International Union of Crystallography The history of crystallographic computing and use of crystallographic software is one which traces the escape from the drudgery of manual human calculations to a world where the user delegates most of the travail to electronic computers. This review traces the development of small-molecule single-crystal and powder diffraction hardware, starting with the use of Hollerith tabulators of the late 1930's through to today's use of high-performance personal computers. It also emphasizes that the main challenge for current and future crystallography computing is not that of hardware development, or even specific scientific challenges, but rather in maintaining a critical mass of human expertise with which these computational challenges can be undertaken. en BEEVERS; COMRIE; ECKERT; HISTORY; HOLLERITH; PAULING; POWDER DIFFRACTION; SINGLE CRYSTAL; SOFTWARE; TEACHING The history of crystallographic computing and use of crystallographic software is one which traces the escape from the drudgery of manual human calculations to a world where the user delegates most of the travail to electronic computers. In practice, this involves practising crystallographers communicating their thoughts to the crystallographic program authors, in the hope that new procedures will be implemented within their software. Against this background, the development of small-molecule single-crystal and powder diffraction software is traced. Starting with the analogue machines and the use of Hollerith tabulators of the late 1930's, it is shown that computing developments have been science led, with new technologies being harnessed to solve pressing crystallographic problems. The development of software is also traced, with a final caution that few of the computations now performed daily are really understood by the program users. Unless a sufficient body of people continues to dismantle and re-build programs, the knowledge encoded in the old programs will become as inaccessible as the knowledge of how to build the Great Pyramid at Giza. text/html Busting out of crystallography's Sisyphean prison: from pencil and paper to structure solving at the press of a button: past, present and future of crystallographic software development, maintenance and distribution text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography 0108-7673 feature articles 65 med@iucr.org 87 http://scripts.iucr.org/cgi-bin/paper?sc5002 Methods of contrast variation are tools that are essential in macromolecular structure research. Anomalous dispersion of X-ray diffraction is widely used in protein crystallography. Recent attempts to extend this method to native resonant labels like sulfur and phosphorus are promising. Substitution of hydrogen isotopes is central to biological applications of neutron scattering. Proton spin polarization considerably enhances an existing contrast prepared by isotopic substitution. Concepts and methods of nuclear magnetic resonance (NMR) become an important ingredient in neutron scattering from dynamically polarized targets. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Stuhrmann, H.B. 2008-01-01 doi:10.1107/S0108767307046569 International Union of Crystallography Originally conceived for protein crystallography, contrast variation has become a favourite tool of small-angle scattering. Recent developments in contrast variation are reviewed. en ANOMALOUS DISPERSION; DYNAMIC NUCLEAR POLARIZATION; ISOTOPIC SUBSTITUTION; UNIQUENESS Methods of contrast variation are tools that are essential in macromolecular structure research. Anomalous dispersion of X-ray diffraction is widely used in protein crystallography. Recent attempts to extend this method to native resonant labels like sulfur and phosphorus are promising. Substitution of hydrogen isotopes is central to biological applications of neutron scattering. Proton spin polarization considerably enhances an existing contrast prepared by isotopic substitution. Concepts and methods of nuclear magnetic resonance (NMR) become an important ingredient in neutron scattering from dynamically polarized targets. text/html Small-angle scattering and its interplay with crystallography, contrast variation in SAXS and SANS text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 181 med@iucr.org 191 http://scripts.iucr.org/cgi-bin/paper?sc5009 This paper summarizes the current state of charge flipping, a recently developed algorithm of ab initio structure determination. Its operation is based on the perturbation of large plateaus of low electron density but not directly on atomicity. Such a working principle radically differs from that of classical direct methods and offers complementary applications. The list of successful structure-solution cases includes periodic and aperiodic crystals using single-crystal and powder diffraction data measured with X-ray and neutron radiation. Apart from counting applications, the paper mainly deals with algorithmic issues: it describes and compares new variants of the iteration scheme, helps to identify and improve solutions, discusses the required data and the use of known information. Finally, it tries to foretell the future of such an alternative among well established direct methods. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Oszlányi, G. Sütő, A. 2008-01-01 doi:10.1107/S0108767307046028 International Union of Crystallography The current state of the charge flipping algorithm is reviewed. en AB INITIO STRUCTURE DETERMINATION; CHARGE FLIPPING ALGORITHM This paper summarizes the current state of charge flipping, a recently developed algorithm of ab initio structure determination. Its operation is based on the perturbation of large plateaus of low electron density but not directly on atomicity. Such a working principle radically differs from that of classical direct methods and offers complementary applications. The list of successful structure-solution cases includes periodic and aperiodic crystals using single-crystal and powder diffraction data measured with X-ray and neutron radiation. Apart from counting applications, the paper mainly deals with algorithmic issues: it describes and compares new variants of the iteration scheme, helps to identify and improve solutions, discusses the required data and the use of known information. Finally, it tries to foretell the future of such an alternative among well established direct methods. text/html The charge flipping algorithm text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 123 med@iucr.org 134 http://scripts.iucr.org/cgi-bin/paper?sc5008 The journals of the International Union of Crystallography have grown in size and number over the past 60 years to match developments in scientific practice and technique. High quality of publication has always been at the forefront of editorial policy and ways in which this has been achieved are described. In particular, the development of standard exchange and archive formats for crystallographic data has allowed the editorial office to conduct automated analyses of structural data supporting articles submitted for publication and these analyses assist the scientific editors in careful and critical peer review. The new information technologies of the Internet age have allowed the IUCr journals to flourish and to provide a wide range of powerful services to authors, editors and readers alike. The integration of literature and supporting structural data is of particular importance. The new technologies have also brought fresh economic and cultural challenges, and offer completely new opportunities to disseminate the results of scientific research. The journals continue to respond to these challenges and take advantage of new opportunities in innovative ways. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Strickland, P.R. McMahon, B. 2008-01-01 doi:10.1107/S0108767307045801 International Union of Crystallography The journal publishing activities of the IUCr over the past 60 years are described, together with the new technological, economic and cultural challenges faced by the journals. Particular emphasis is placed on the role of innovative publishing technologies in ensuring the quality of the published information and in providing effective access to the data underpinning the scientific results. en CRYSTALLOGRAPHIC PUBLISHING; IUCR JOURNALS The journals of the International Union of Crystallography have grown in size and number over the past 60 years to match developments in scientific practice and technique. High quality of publication has always been at the forefront of editorial policy and ways in which this has been achieved are described. In particular, the development of standard exchange and archive formats for crystallographic data has allowed the editorial office to conduct automated analyses of structural data supporting articles submitted for publication and these analyses assist the scientific editors in careful and critical peer review. The new information technologies of the Internet age have allowed the IUCr journals to flourish and to provide a wide range of powerful services to authors, editors and readers alike. The integration of literature and supporting structural data is of particular importance. The new technologies have also brought fresh economic and cultural challenges, and offer completely new opportunities to disseminate the results of scientific research. The journals continue to respond to these challenges and take advantage of new opportunities in innovative ways. text/html Crystallographic publishing in the electronic age text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 38 med@iucr.org 51 http://scripts.iucr.org/cgi-bin/paper?sc5006 Mathematical crystallography is the branch of crystallography dealing specifically with the fundamental properties of symmetry and periodicity of crystals, topological properties of crystal structures, twins, modular and modulated structures, polytypes and OD structures, as well as the symmetry aspects of phase transitions and physical properties of crystals. Mathematical crystallography has had its most evident success with the development of the theory of space groups at the end of the XIX century; since then, it has greatly enlarged its applications, but crystallographers are not always familiar with the developments that followed, partly because the applications sometimes require some additional background that the structural crystallographer does not always possess (as is the case, for example, in graph theory). The knowledge offered by mathematical crystallography is at present only partly mirrored in International Tables for Crystallography and is sometimes still enshrined in more specialist texts and publications. To cover this communication gap is one of the tasks of the IUCr Commission on Mathematical and Theoretical Crystallography (MaThCryst). Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Nespolo, M. 2008-01-01 doi:10.1107/S0108767307044625 International Union of Crystallography A survey of some of the main topics of mathematical crystallography is presented, together with the challenges for future developments. en GRAPH THEORY; MATHEMATICAL CRYSTALLOGRAPHY; OD STRUCTURES; POLYTYPES; SYMMETRY; THEORETICAL CRYSTALLOGRAPHY; TOPOLOGY; TWINS Mathematical crystallography is the branch of crystallography dealing specifically with the fundamental properties of symmetry and periodicity of crystals, topological properties of crystal structures, twins, modular and modulated structures, polytypes and OD structures, as well as the symmetry aspects of phase transitions and physical properties of crystals. Mathematical crystallography has had its most evident success with the development of the theory of space groups at the end of the XIX century; since then, it has greatly enlarged its applications, but crystallographers are not always familiar with the developments that followed, partly because the applications sometimes require some additional background that the structural crystallographer does not always possess (as is the case, for example, in graph theory). The knowledge offered by mathematical crystallography is at present only partly mirrored in International Tables for Crystallography and is sometimes still enshrined in more specialist texts and publications. To cover this communication gap is one of the tasks of the IUCr Commission on Mathematical and Theoretical Crystallography (MaThCryst). text/html Does mathematical crystallography still have a role in the XXI century? text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 96 med@iucr.org 111 http://scripts.iucr.org/cgi-bin/paper?sc5010 An account is given of the development of the SHELX system of computer programs from SHELX-76 to the present day. In addition to identifying useful innovations that have come into general use through their implementation in SHELX, a critical analysis is presented of the less-successful features, missed opportunities and desirable improvements for future releases of the software. An attempt is made to understand how a program originally designed for photographic intensity data, punched cards and computers over 10000 times slower than an average modern personal computer has managed to survive for so long. SHELXL is the most widely used program for small-molecule refinement and SHELXS and SHELXD are often employed for structure solution despite the availability of objectively superior programs. SHELXL also finds a niche for the refinement of macromolecules against high-resolution or twinned data; SHELXPRO acts as an interface for macromolecular applications. SHELXC, SHELXD and SHELXE are proving useful for the experimental phasing of macromolecules, especially because they are fast and robust and so are often employed in pipelines for high-throughput phasing. This paper could serve as a general literature citation when one or more of the open-source SHELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Sheldrick, G.M. 2008-01-01 doi:10.1107/S0108767307043930 International Union of Crystallography The SHELX programs for crystal structure determination are reviewed by their author. en COMPUTER PROGRAMS; CRYSTAL STRUCTURE DETERMINATION; PHASING; SHELX; STRUCTURE REFINEMENT An account is given of the development of the SHELX system of computer programs from SHELX-76 to the present day. In addition to identifying useful innovations that have come into general use through their implementation in SHELX, a critical analysis is presented of the less-successful features, missed opportunities and desirable improvements for future releases of the software. An attempt is made to understand how a program originally designed for photographic intensity data, punched cards and computers over 10000 times slower than an average modern personal computer has managed to survive for so long. SHELXL is the most widely used program for small-molecule refinement and SHELXS and SHELXD are often employed for structure solution despite the availability of objectively superior programs. SHELXL also finds a niche for the refinement of macromolecules against high-resolution or twinned data; SHELXPRO acts as an interface for macromolecular applications. SHELXC, SHELXD and SHELXE are proving useful for the experimental phasing of macromolecules, especially because they are fast and robust and so are often employed in pipelines for high-throughput phasing. This paper could serve as a general literature citation when one or more of the open-source SHELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination. text/html A short history of SHELX text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 112 med@iucr.org 122 http://scripts.iucr.org/cgi-bin/paper?sc5011 Following the seminal work of Von Dreele, powder X-ray diffraction studies on proteins are being established as a valuable complementary technique to single-crystal measurements. A wide range of small proteins have been found to give synchrotron powder diffraction profiles where the peak widths are essentially limited only by the instrumental resolution. The rich information contained in these profiles, combined with developments in data analysis, has stimulated research and development to apply the powder technique to microcrystalline protein samples. In the present work, progress in using powder diffraction for macromolecular crystallography is reported. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Margiolaki, I. Wright, J.P. 2008-01-01 doi:10.1107/S0108767307043735 International Union of Crystallography The last 10 years have seen a revolution in powder crystallography; macromolecules can now be studied using powder samples. When large single crystals are not available then crystallographic information may be obtained from a polycrystalline powder instead. en POWDER DIFFRACTION; PROTEIN CRYSTALLOGRAPHY; SYNCHROTRON RADIATION Following the seminal work of Von Dreele, powder X-ray diffraction studies on proteins are being established as a valuable complementary technique to single-crystal measurements. A wide range of small proteins have been found to give synchrotron powder diffraction profiles where the peak widths are essentially limited only by the instrumental resolution. The rich information contained in these profiles, combined with developments in data analysis, has stimulated research and development to apply the powder technique to microcrystalline protein samples. In the present work, progress in using powder diffraction for macromolecular crystallography is reported. text/html Powder crystallography on macromolecules text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 169 med@iucr.org 180 http://scripts.iucr.org/cgi-bin/paper?sc5005 Neutron diffraction provides an experimental method of directly locating H atoms in proteins, a technique complementary to ultra-high-resolution X-ray diffraction. Three different types of neutron diffractometers for biological macromolecules have been constructed in Japan, France and the USA, and they have been used to determine the crystal structures of proteins up to resolution limits of 1.5–2.5 Å. Results relating to H-atom positions and hydration patterns in proteins have been obtained from these studies. Examples include the geometrical details of hydrogen bonds, the role of H atoms in enzymatic activity, CH3 configuration, H/D exchange in proteins and oligonucleotides, and the dynamical behavior of hydration structures, all of which have been extracted from these structural results and reviewed. Other techniques, such as the growth of large single crystals and a database of hydrogen and hydration in proteins, are described. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Niimura, N. Bau, R. 2008-01-01 doi:10.1107/S0108767307043498 International Union of Crystallography Several results from neutron protein crystallography relating H-atom positions and hydration patterns in proteins and oligonucleotides are reviewed. en BIOLOGICAL MACROMOLECULES; FOLDING STRUCTURE; NEUTRON PROTEIN CRYSTALLOGRAPHY Neutron diffraction provides an experimental method of directly locating H atoms in proteins, a technique complementary to ultra-high-resolution X-ray diffraction. Three different types of neutron diffractometers for biological macromolecules have been constructed in Japan, France and the USA, and they have been used to determine the crystal structures of proteins up to resolution limits of 1.5–2.5 Å. Results relating to H-atom positions and hydration patterns in proteins have been obtained from these studies. Examples include the geometrical details of hydrogen bonds, the role of H atoms in enzymatic activity, CH3 configuration, H/D exchange in proteins and oligonucleotides, and the dynamical behavior of hydration structures, all of which have been extracted from these structural results and reviewed. Other techniques, such as the growth of large single crystals and a database of hydrogen and hydration in proteins, are described. text/html Neutron protein crystallography: beyond the folding structure of biological macromolecules text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 12 med@iucr.org 22 http://scripts.iucr.org/cgi-bin/paper?sc5007 Studies of diffuse scattering had a prominent place in the first issue of Acta Crystallographica 60 years ago at a time when conventional crystallography (determination of the average structure from Bragg peaks) was in its infancy. Since that time, conventional crystallography has developed enormously while diffuse-scattering analysis has seemingly lagged well behind. The paper highlights some of the extra difficulties involved in the measurement, interpretation and analysis of diffuse scattering and plots the progress that has been made. With the advent of the latest X-ray and neutron sources, area detectors and the ever-increasing power of computers, most disorder problems are now tractable. Two recent contrasting examples are described which highlight what can be achieved by current methods. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Welberry, T.R. Goossens, D.J. 2008-01-01 doi:10.1107/S0108767307041918 International Union of Crystallography The paper highlights some of the extra difficulties involved in the measurement, interpretation and analysis of diffuse scattering relative to the methods of conventional crystallography and plots the progress that has been made in the lifetime of Acta Crystallographica. With the advent of the latest X-ray and neutron sources, area detectors and the ever-increasing power of computers, most diffuse scattering and disorder problems are now tractable. en DIFFUSE SCATTERING; MONTE CARLO METHODS Studies of diffuse scattering had a prominent place in the first issue of Acta Crystallographica 60 years ago at a time when conventional crystallography (determination of the average structure from Bragg peaks) was in its infancy. Since that time, conventional crystallography has developed enormously while diffuse-scattering analysis has seemingly lagged well behind. The paper highlights some of the extra difficulties involved in the measurement, interpretation and analysis of diffuse scattering and plots the progress that has been made. With the advent of the latest X-ray and neutron sources, area detectors and the ever-increasing power of computers, most disorder problems are now tractable. Two recent contrasting examples are described which highlight what can be achieved by current methods. text/html The interpretation and analysis of diffuse scattering using Monte Carlo simulation methods text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 23 med@iucr.org 32 http://scripts.iucr.org/cgi-bin/paper?pf0062 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Paufler, P. 2007-11-01 doi:10.1107/S0108767307041207 International Union of Crystallography en BOOK REVIEW text/html Complete online set of International tables for crystallography, Vols. A–G. Edited by H. Fuess, Th. Hahn, H. Wondratschek, U. Müller, U. Shmueli, E. Prince, A. Authier, V. Kopský, D. B. Litvin, M. G. Rossmann, E. Arnold, S. Hall and B. McMahon. Springer, jointly published with the IUCr, 2007. Price for online access USD 2080.00. eISBN: 978-1-4020-5259-0, doi: 10.1107/97809553602060000001, http://it.iucr.org. text 6 63 2007-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 book reviews 483 med@iucr.org 483 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sc5001 Crystallographic Nexus CD-ROMs, containing a range of free crystallographic software for single-crystal and powder diffraction available on the Internet, have been distributed on request since 1996. The free CD is made in the form of a `virtual Internet' with the main intent of benefiting crystallographers with inadequate Internet access. The IUCr funds an annual/biennial update which is distributed to known previous recipients. Feedback from current recipients indicates the CD is still useful. The most current IUCr-funded CD is being produced by the CCP14 project at University College London and The Royal Institution UK for distribution to the ECM 2007 and AsCA 2007 conferences. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Cranswick, L.M.D. Bisson, W. Cockcroft, J.K. 2008-01-01 doi:10.1107/S0108767307040573 International Union of Crystallography Crystallographic Nexus CD-ROMs, containing a range of free crystallographic software for single-crystal and powder diffraction available on the Internet, have been distributed free on request since 1996. The free CD is made in the form of a `virtual Internet' with the main intent of benefiting crystallographers with inadequate Internet access. en CD-ROM; CRYSTALLOGRAPHIC SOFTWARE; INTERNET; POWDER DIFFRACTION; SINGLE CRYSTAL Crystallographic Nexus CD-ROMs, containing a range of free crystallographic software for single-crystal and powder diffraction available on the Internet, have been distributed on request since 1996. The free CD is made in the form of a `virtual Internet' with the main intent of benefiting crystallographers with inadequate Internet access. The IUCr funds an annual/biennial update which is distributed to known previous recipients. Feedback from current recipients indicates the CD is still useful. The most current IUCr-funded CD is being produced by the CCP14 project at University College London and The Royal Institution UK for distribution to the ECM 2007 and AsCA 2007 conferences. text/html Nexus, crystallographic computing all around the world text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 214 med@iucr.org 217 http://scripts.iucr.org/cgi-bin/paper?es0361 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Helliwell, J.R. Abrahams, S.C. 2007-09-01 doi:10.1107/S0108767307039062 International Union of Crystallography en OBITUARIES text/html Durward William John Cruickshank (1924–2007) text 5 63 2007-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 obituaries 375 med@iucr.org 379 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sc5003 It took Dan Shechtman more than two years to get his discovery of an Al–Mn phase with icosahedral diffraction symmetry and sharp Bragg reflections published. A paradigm shift had to take place before this novel ordering state of matter – seemingly contradicting crystallographic laws – could be accepted. Today, more than 25 years later, the existence of quasicrystals is beyond doubt. However, not everything is settled yet. All the factors governing formation, growth, stability and structure of quasicrystals are still not fully understood, nor is it resolved whether their structures are strictly or only on average quasiperiodic, and it is still an open question why only quasicrystals with 5-, 8-, 10- and 12-fold rotational symmetry have been experimentally observed so far. These points will be addressed in this review article. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Steurer, W. Deloudi, S. 2008-01-01 doi:10.1107/S0108767307038627 International Union of Crystallography The state of the art of structure research on quasicrystals is reviewed. Some questions concerning formation, growth and stability are addressed. en DECAGONAL PHASES; ICOSAHEDRAL PHASES; N-DIMENSIONAL APPROACH; PHOTONIC QUASICRYSTALS; QUASICRYSTALS It took Dan Shechtman more than two years to get his discovery of an Al–Mn phase with icosahedral diffraction symmetry and sharp Bragg reflections published. A paradigm shift had to take place before this novel ordering state of matter – seemingly contradicting crystallographic laws – could be accepted. Today, more than 25 years later, the existence of quasicrystals is beyond doubt. However, not everything is settled yet. All the factors governing formation, growth, stability and structure of quasicrystals are still not fully understood, nor is it resolved whether their structures are strictly or only on average quasiperiodic, and it is still an open question why only quasicrystals with 5-, 8-, 10- and 12-fold rotational symmetry have been experimentally observed so far. These points will be addressed in this review article. text/html Fascinating quasicrystals text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 1 med@iucr.org 11 http://scripts.iucr.org/cgi-bin/paper?sh0188 Both the approach used and the progress made in the assignment of structure types to the crystal structures contained in the ICSD database are reported. Extending earlier work, an hierarchical set of criteria for the separation of isopointal structures into isoconfigurational structure types is used. It is shown how these criteria, which include the space group (number), Wyckoff sequence and Pearson symbol, c/a ratio, β ranges, ANX formulae and, in certain cases, the necessary elements and forbidden elements, may be used to uniquely identify the representative structure types of the compounds contained in the ICSD database. Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Allmann, R. Hinek, R. 2007-09-01 doi:10.1107/S0108767307038081 International Union of Crystallography The approach used and the progress made in the assignment of structure types to the crystal structures contained in the ICSD database are reported. en INORGANIC CRYSTAL STRUCTURE DATABASE; ICSD; STRUCTURE TYPES Both the approach used and the progress made in the assignment of structure types to the crystal structures contained in the ICSD database are reported. Extending earlier work, an hierarchical set of criteria for the separation of isopointal structures into isoconfigurational structure types is used. It is shown how these criteria, which include the space group (number), Wyckoff sequence and Pearson symbol, c/a ratio, β ranges, ANX formulae and, in certain cases, the necessary elements and forbidden elements, may be used to uniquely identify the representative structure types of the compounds contained in the ICSD database. text/html The introduction of structure types into the Inorganic Crystal Structure Database ICSD text 5 63 2007-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 research papers 412 med@iucr.org 417 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sc5004 The Protein Data Bank began as a grassroots effort in 1971. It has grown from a small archive containing a dozen structures to a major international resource for structural biology containing more than 40000 entries. The interplay of science, technology and attitudes about data sharing have all played a role in the growth of this resource. Copyright (c) 2008 International Union of Crystallography urn:issn:0108-7673 Berman, H.M. 2008-01-01 doi:10.1107/S0108767307035623 International Union of Crystallography Since 1971, the Protein Data Bank archive of biological macromolecules has been a community-driven resource for science and education worldwide. en DATABASES; HISTORY OF PDB; NUCLEIC ACIDS; POLICY RELATIVE TO PDB; PROTEINS The Protein Data Bank began as a grassroots effort in 1971. It has grown from a small archive containing a dozen structures to a major international resource for structural biology containing more than 40000 entries. The interplay of science, technology and attitudes about data sharing have all played a role in the growth of this resource. text/html The Protein Data Bank: a historical perspective text 1 64 2008-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2008 International Union of Crystallography 0108-7673 feature articles 88 med@iucr.org 95 http://scripts.iucr.org/cgi-bin/paper?pf0051 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Röhr, C. 2007-07-01 doi:10.1107/S0108767307027250 International Union of Crystallography en BOOK REVIEW text/html Structure and chemistry of crystalline solids. By B. Douglas and S.-M. Ho. Pp. X + 346. New York: Springer 2006. Price (hardcover) EUR 106.95. ISBN 978-0-387-26147-8. text 4 63 2007-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 book reviews 374 med@iucr.org 374 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0034 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Paufler, P.P. 2007-07-01 doi:10.1107/S0108767307021344 International Union of Crystallography en BOOK RECEIVED text/html The chemical bond in inorganic chemistry. The bond valence model. By I. David Brown. Pp. 278. Oxford: Oxford University Press, 2006. Price (paperback) GBP 35.00. ISBN 0-19-929881-5. text 4 63 2007-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 books received 374 med@iucr.org 374 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0948 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Helliwell, J.R. 2007-09-01 doi:10.1107/S0108767307019125 International Union of Crystallography en BOOK REVIEW text/html Personal X-ray reflections. By U. W. Arndt. Pp. 177. Twickenham: Athena Press, 2006. Price GBP 6.99, USD 11.95. ISBN 1-84401-694-3. text 5 63 2007-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 book reviews 439 med@iucr.org 440 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh9049 In the paper by Livet [Acta Cryst. (2007), A63, 63–87], equation (15) is incorrect. The correct equation is \beta(z) = \left\{\textstyle\sum\limits_{n = 0}^{\infty} (-1){}^n 2^{2n+2}z^{2n}/[(2n+1)(2n+2){}^2(2n+1)!]\right\}^2.\eqno(15) Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Livet, F. 2007-05-01 doi:10.1107/S0108767307016248 International Union of Crystallography Erratum to Livet [Acta Cryst. (2007), A63, 63–87]. en COHERENT X-RAY BEAMS; DYNAMICS OF FLUCTUATIONS; LENSLESS IMAGING; SMALL-ANGLE SET-UPS In the paper by Livet [Acta Cryst. (2007), A63, 63–87], equation (15) is incorrect. The correct equation is \beta(z) = \left\{\textstyle\sum\limits_{n = 0}^{\infty} (-1){}^n 2^{2n+2}z^{2n}/[(2n+1)(2n+2){}^2(2n+1)!]\right\}^2.\eqno(15) text/html Diffraction with a coherent X-ray beam: dynamics and imaging. Erratum text 3 63 2007-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 addenda and errata 287 med@iucr.org 287 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0045 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Paufler, P. 2007-05-01 doi:10.1107/S0108767307011506 International Union of Crystallography en BOOK RECEIVED text/html Handbook of X-ray data. By G. Zschornack. Pp. IX + 967. Berlin: Springer-Verlag, 2007. Price (hardback) EUR 213.95. ISBN 978-3-540-28618-9. text 3 63 2007-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 books received 288 med@iucr.org 288 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh5054 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Spackman, M.A. 2007-03-01 doi:10.1107/S0108767307001298 International Union of Crystallography Comment on Volkov, King, Coppens & Farrugia [Acta Cryst. (2006), A62, 400–408]. en ASPHERICAL PSEUDOATOM MODEL; ELECTRIC FIELD; ELECTRIC FIELD GRADIENT; ELECTROSTATIC POTENTIAL text/html Comment on On the calculation of the electrostatic potential, electric field and electric field gradient from the aspherical pseudoatom model by Volkov, King, Coppens & Farrugia (2006) text 2 63 2007-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 letters to the editor 198 med@iucr.org 200 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh0187 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Volkov, A. Coppens, P. 2007-03-01 doi:10.1107/S0108767307002620 International Union of Crystallography Response to Spackman's comment on Volkov, King, Coppens & Farrugia [Acta Cryst. (2006), A62, 400–408]. en text/html Response to Spackman's comment on On the calculation of the electrostatic potential, electric field and electric field gradient from the aspherical pseudoatom model text 2 63 2007-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 letters to the editor 201 med@iucr.org 203 1600-5724 http://scripts.iucr.org/cgi-bin/paper?dm5003 The general approach for describing and designing complex hierarchical icosahedral structures is discussed. Structural models of icosahedral carbon nanoparticles in which the local arrangement of atoms is virtually identical to that in diamond are derived. It is shown that icosahedral diamond-like particles can be transformed into onion-like shell structures (and vice versa) by the consecutive smoothing (puckering) of atomic networks without disturbance of their topological integrity. The possibility of coherent coexistence of icosahedral diamond-like core with onion shells is shown. Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Shevchenko, V.Ya. Madison, A.E. Mackay, A.L. 2007-03-01 doi:10.1107/S0108767307002723 International Union of Crystallography In icosahedral carbon nanoparticles, the diamond-like core can undergo a reversible topological transition into and coexist coherently with the onion shells. en CARBON ONION; COHERENT COEXISTENCE; NANODIAMOND The general approach for describing and designing complex hierarchical icosahedral structures is discussed. Structural models of icosahedral carbon nanoparticles in which the local arrangement of atoms is virtually identical to that in diamond are derived. It is shown that icosahedral diamond-like particles can be transformed into onion-like shell structures (and vice versa) by the consecutive smoothing (puckering) of atomic networks without disturbance of their topological integrity. The possibility of coherent coexistence of icosahedral diamond-like core with onion shells is shown. text/html Coherent coexistence of nanodiamonds and carbon onions in icosahedral core-shell particles text 2 63 2007-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 research papers 172 med@iucr.org 176 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh5049 Methods for carrying out coherent X-ray scattering experiments are reviewed. The brilliance of the available synchrotron sources, the characteristics of the existing optics, the various ways of obtaining a beam of controlled coherence properties and the detectors used are summarized. Applications in the study of the dynamics of speckle patterns are described. In the case of soft condensed matter, the movement of inclusions like fillers in polymers or colloidal particles can be observed and these can reflect polymer or liquid-crystal fluctuations. In hard condensed-matter problems, like phase transitions, charge-density waves or phasons in quasicrystals, the study of speckle fluctuations provides new time-resolved methods. In the domain of lensless imaging, the coherent beam gives the modulus of the sample Fourier transform. If oversampling conditions are fulfilled, the phase can be obtained and the image in the direct space can be reconstructed. The forthcoming improvements of all these techniques are discussed. Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Livet, F. 2007-03-01 doi:10.1107/S010876730605570X International Union of Crystallography Techniques for coherent X-ray scattering measurements are detailed. Applications in the study of the dynamics of fluctuations and in lensless high-resolution imaging are described. en COHERENT X-RAY BEAMS; DYNAMICS OF FLUCTUATIONS; LENSLESS IMAGING; SMALL-ANGLE SET-UPS Methods for carrying out coherent X-ray scattering experiments are reviewed. The brilliance of the available synchrotron sources, the characteristics of the existing optics, the various ways of obtaining a beam of controlled coherence properties and the detectors used are summarized. Applications in the study of the dynamics of speckle patterns are described. In the case of soft condensed matter, the movement of inclusions like fillers in polymers or colloidal particles can be observed and these can reflect polymer or liquid-crystal fluctuations. In hard condensed-matter problems, like phase transitions, charge-density waves or phasons in quasicrystals, the study of speckle fluctuations provides new time-resolved methods. In the domain of lensless imaging, the coherent beam gives the modulus of the sample Fourier transform. If oversampling conditions are fulfilled, the phase can be obtained and the image in the direct space can be reconstructed. The forthcoming improvements of all these techniques are discussed. text/html Diffraction with a coherent X-ray beam: dynamics and imaging text 2 63 2007-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 lead articles 87 med@iucr.org 107 1600-5724 http://scripts.iucr.org/cgi-bin/paper?es0359 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 2007-01-01 doi:10.1107/S0108767306053992 International Union of Crystallography en text/html Nominations for the Ewald Prize text 1 63 2007-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 international union of crystallography 80 med@iucr.org 80 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0041 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Paufler, P. 2007-05-01 doi:10.1107/S010876730701149X International Union of Crystallography en BOOK RECEIVED text/html Structure and chemistry of crystalline solids. By B. E. Douglas and S.-M. Ho. Pp. x + 346. New York: Springer Science and Business Media, 2006. Price (hardback) EUR 99.95, USD 129.00, GBP 77.00. ISBN 978-0-387-26147-8. text 3 63 2007-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 books received 288 med@iucr.org 288 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0038 Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Paufler, P. 2007-05-01 doi:10.1107/S0108767306047349 International Union of Crystallography en BOOK RECEIVED text/html Structure determination from powder diffraction data. International Union of Crystallography Monographs in Crystallography. No. 13. Edited by W. I. F. David, K. Shankland, L. B. McCusker and Ch. Baerlocher. Pp. xix + 337. Oxford University Press, 2006. Price (paperback) GBP 39.95. ISBN 978-0-19-920553-0. text 3 63 2007-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 books received 288 med@iucr.org 288 1600-5724 http://scripts.iucr.org/cgi-bin/paper?au5046 Multiple twinning in cubic crystals is represented geometrically by a three-dimensional fractal and algebraically by a groupoid. In this groupoid, the variant crystals are the objects, the misorientations between the variants are the operations, and the Σ3n operators are the different types of operations (expressed by sets of equivalent operations). A general formula gives the number of variants and the number of Σ3n operators for any twinning order. Different substructures of this groupoid (free group, semigroup) can be equivalently introduced to encode the operations with strings. For any coding substructure, the operators are expressed by sets of equivalent strings. The composition of two operators is determined without any matrix calculation by string concatenations. It is multivalued due to the groupoid structure. The composition table of the operators is used to identify the Σ3n grain boundaries and to reconstruct the twin related domains in the electron back-scattered diffraction maps. Copyright (c) 2007 International Union of Crystallography urn:issn:0108-7673 Cayron, C. 2007-01-01 doi:10.1107/S0108767306044291 International Union of Crystallography Multiple twinning in cubic crystals is represented geometrically by three-dimensional fractals and algebraically by groupoids. The groupoid composition table can be used to identify the Σ3n grain boundaries in EBSD maps. en ELECTRON BACK-SCATTER DIFFRACTION (EBSD); FRACTAL; GROUPOID; MULTIPLE TWINNING; TWIN RELATED DOMAIN (TRD) Multiple twinning in cubic crystals is represented geometrically by a three-dimensional fractal and algebraically by a groupoid. In this groupoid, the variant crystals are the objects, the misorientations between the variants are the operations, and the Σ3n operators are the different types of operations (expressed by sets of equivalent operations). A general formula gives the number of variants and the number of Σ3n operators for any twinning order. Different substructures of this groupoid (free group, semigroup) can be equivalently introduced to encode the operations with strings. For any coding substructure, the operators are expressed by sets of equivalent strings. The composition of two operators is determined without any matrix calculation by string concatenations. It is multivalued due to the groupoid structure. The composition table of the operators is used to identify the Σ3n grain boundaries and to reconstruct the twin related domains in the electron back-scattered diffraction maps. text/html Multiple twinning in cubic crystals: geometric/algebraic study and its application for the identification of the Σ3n grain boundaries text 1 63 2007-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2007 International Union of Crystallography 0108-7673 research papers 11 med@iucr.org 29 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh5048 Accurate, yet simple and efficient, formulae are presented for calculation of the electrostatic potential (ESP), electric field (EF) and electric field gradient (EFG) from the aspherical Hansen–Coppens pseudoatom model of electron density [Hansen & Coppens (1978). Acta Cryst. A34, 909–921]. They are based on the expansion of |r′ − r|−1 in spherical harmonics and the incomplete gamma function for a Slater-type function of the form Rl(r) = rn exp(−αr). The formulae are valid for 0 ≤ r ≤ ∞ and are easily extended to higher values of l. Special treatment of integrals is needed only for functions with n = l and n = l + 1 at r = 0. The method is tested using theoretical pseudoatom parameters of the formamide molecule obtained via reciprocal-space fitting of PBE/6-31G** densities and experimental X-ray data of Fe(CO)5. The ESP, EF and EFG values at the nuclear positions in formamide are in very good agreement with those directly evaluated from density-functional PBE calculations with 6-31G**, aug-cc-pVDZ and aug-cc-pVTZ basis sets. The small observed discrepancies are attributed to the different behavior of Gaussian- and Slater-type functions near the nuclei and to imperfections of the reciprocal-space fit. An EF map is displayed which allows useful visualization of the lattice EF effects in the crystal structure of formamide. Analysis of experimental 100 K X-ray data of Fe(CO)5 yields the value of the nuclear quadrupole moment Q(57Fem) = 0.12 × 10−28 m2 after taking into account Sternheimer shielding/antishielding effects of the core. This value is in excellent agreement with that reported by Su & Coppens [Acta Cryst. (1996), A52, 748–756] but slightly smaller than the generally accepted value of 0.16 ± 5% × 10−28 m2 obtained from combined theoretical/spectroscopic studies [Dufek, Blaha & Schwarz (1995). Phys. Rev. Lett. 25, 3545–3548]. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Volkov, A. King, H.F. Coppens, P. Farrugia, L.J. 2006-09-01 doi:10.1107/S0108767306026298 International Union of Crystallography Accurate, simple and efficient formulae for calculation of the electrostatic potential, electric field and electric field gradient from the aspherical pseudoatom model of electron density are presented. The expressions are applied to the determination of the nuclear quadrupole moment of the Fe atom in Fe(CO)5. en ASPHERICAL PSEUDOATOM MODEL; ELECTRIC FIELD; ELECTRIC FIELD GRADIENT; ELECTROSTATIC POTENTIAL Accurate, yet simple and efficient, formulae are presented for calculation of the electrostatic potential (ESP), electric field (EF) and electric field gradient (EFG) from the aspherical Hansen–Coppens pseudoatom model of electron density [Hansen & Coppens (1978). Acta Cryst. A34, 909–921]. They are based on the expansion of |r′ − r|−1 in spherical harmonics and the incomplete gamma function for a Slater-type function of the form Rl(r) = rn exp(−αr). The formulae are valid for 0 ≤ r ≤ ∞ and are easily extended to higher values of l. Special treatment of integrals is needed only for functions with n = l and n = l + 1 at r = 0. The method is tested using theoretical pseudoatom parameters of the formamide molecule obtained via reciprocal-space fitting of PBE/6-31G** densities and experimental X-ray data of Fe(CO)5. The ESP, EF and EFG values at the nuclear positions in formamide are in very good agreement with those directly evaluated from density-functional PBE calculations with 6-31G**, aug-cc-pVDZ and aug-cc-pVTZ basis sets. The small observed discrepancies are attributed to the different behavior of Gaussian- and Slater-type functions near the nuclei and to imperfections of the reciprocal-space fit. An EF map is displayed which allows useful visualization of the lattice EF effects in the crystal structure of formamide. Analysis of experimental 100 K X-ray data of Fe(CO)5 yields the value of the nuclear quadrupole moment Q(57Fem) = 0.12 × 10−28 m2 after taking into account Sternheimer shielding/antishielding effects of the core. This value is in excellent agreement with that reported by Su & Coppens [Acta Cryst. (1996), A52, 748–756] but slightly smaller than the generally accepted value of 0.16 ± 5% × 10−28 m2 obtained from combined theoretical/spectroscopic studies [Dufek, Blaha & Schwarz (1995). Phys. Rev. Lett. 25, 3545–3548]. text/html On the calculation of the electrostatic potential, electric field and electric field gradient from the aspherical pseudoatom model text 5 62 2006-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 research papers 400 med@iucr.org 408 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0035 Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Authier, A. 2006-11-01 doi:10.1107/S010876730602616X International Union of Crystallography en BOOK REVIEW text/html Cristallographie. Deuxième édition, revue et augmentée. By D. Schwarzenbach and G. Chapuis. Lausanne: Presses Polytechniques et Universitaires Romandes, 2006. Pp. x + 344. In French. Price (softcover) CHF 79.50 (Switzerland), EUR 55.45 (other countries). ISBN 2-88074-672-8. text 6 62 2006-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 book reviews 464 med@iucr.org 464 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0032 Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Goddard, R. 2006-11-01 doi:10.1107/S0108767306023348 International Union of Crystallography en BOOK REVIEW text/html International tables for crystallography, Vol. G: Definition and exchange of crystallographic data. Edited by Sydney Hall and Brian McMahon. Dordrecht: Springer, 2005. Pp. xii + 594. Price (hardback) EUR 205.00, USD 220.00, GBP 135.00 for institutions; EUR 102.50, USD 110.00, GBP 67.50 for individuals. ISBN 1-4020-3138-6. text 6 62 2006-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 book reviews 463 med@iucr.org 464 1600-5724 http://scripts.iucr.org/cgi-bin/paper?lb5002 Molecular dynamics computer simulation models are employed to study the direct filling of single-walled carbon nanotubes (which vary in diameter) with an archetypal metal trihalide, LaCl3. The use of relatively simple potential models allows the investigation of details of both the atomistic filling mechanism and the thermodynamic factors controlling the formation. The resulting low-dimensional crystallites are analysed with respect to bulk crystal structures and compared to experimental high-resolution transmission-electron-microscopy images by simulation of equivalent micrographs from one of the obtained potential models, resulting in excellent agreement between the simulated and experimental images. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Wilson, M. Friedrichs, S. 2006-07-01 doi:10.1107/S0108767306018101 International Union of Crystallography An MX3 stoichiometry salt, LaCl3, is shown to fill carbon nanotubes, of varying diameter, via molecular dynamics computer simulations to produce low-dimension crystals. The filled crystal structures allow a full atomistic comparison to be made with experimental high-resolution transmission electron micrographs, and the emergence of new, non-bulk, crystal structures is predicted. en CARBON NANOTUBES; METAL TRIHALIDES Molecular dynamics computer simulation models are employed to study the direct filling of single-walled carbon nanotubes (which vary in diameter) with an archetypal metal trihalide, LaCl3. The use of relatively simple potential models allows the investigation of details of both the atomistic filling mechanism and the thermodynamic factors controlling the formation. The resulting low-dimensional crystallites are analysed with respect to bulk crystal structures and compared to experimental high-resolution transmission-electron-microscopy images by simulation of equivalent micrographs from one of the obtained potential models, resulting in excellent agreement between the simulated and experimental images. text/html The formation of low-dimensional metal trihalide crystals in carbon nanotubes text 4 62 2006-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 research papers 287 med@iucr.org 295 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0030 Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Paufler, P.P. 2006-07-01 doi:10.1107/S0108767306014826 International Union of Crystallography en BOOK RECEIVED text/html Cristallographie. Deuxième édition revue et augmentée. Par Dieter Schwarzenbach et Gervais Chapuis. Paris: Presses Polytechniques et Universitaires Romandes, 2006. Pp. xii + 344. Prix broché EUR 55.45. ISBN 2-88074-672-8. text 4 62 2006-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 books received 318 med@iucr.org 318 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0029 Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Paufler, P.P. 2006-07-01 doi:10.1107/S0108767306014814 International Union of Crystallography en BOOK RECEIVED text/html Franz Ernst Neumann (1798–1895). Zum 200. Geburtstag des Mathematikers, Physikers und Kristallographen. Herausgeber R. Fritsch, E. Neumann-Redlin-von Neumann und T. J. Schenck. (Bilingual German/Russian.) Kaliningrad und München: Terra Baltica und Ludwig-Maximilians-Universität, 2005. 252 Seiten. Broschiert Preis: EUR 10. ISBN 5-98777-005-X, 3-922480-17-9. text 4 62 2006-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 books received 318 med@iucr.org 318 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0001 Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Paufler, P. 2006-07-01 doi:10.1107/S0108767306012001 International Union of Crystallography en BOOK REVIEW text/html International tables for crystallography, Vol. D: Physical properties of crystals. Edited by André Authier. Dordrecht/Boston/London: Kluwer Academic Publishers, 2003. Pp. 522 + xii + CD-ROM. Price GBP 135, EUR 205, USD 220. ISBN 1-4020-0714-0. text 4 62 2006-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 book reviews 316 med@iucr.org 318 1600-5724 http://scripts.iucr.org/cgi-bin/paper?es0350 Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Cruickshank, D. 2006-05-01 doi:10.1107/S0108767306005563 International Union of Crystallography en OBITUARY text/html Robert Crispin Evans (1909–2005) text 3 62 2006-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 obituaries 147 med@iucr.org 151 1600-5724 http://scripts.iucr.org/cgi-bin/paper?xo5008 The theory of domain states is reviewed as a prerequisite for consideration of tensorial distinction of domain states. It is then shown that the parameters of the first domain in a ferroic phase transition from a set of isomorphic groups of the same oriented Laue class can be systematically and suitably represented in terms of typical variables. On replacing these variables by actual tensor components according to the previous paper [Kopský (2006), Acta Cryst. A62, 47–64], we can reveal the tensorial parameters associated with each particular symmetry descent. Parameters are distinguished by the ireps to which they belong and this can be used to determine which of them are the principal parameters that distinguish all domain states, in contrast to secondary parameters which are common to several domain states. In general, the parameters are expressed as the covariant components of the tensors. A general procedure is described which is designed to transform the results to Cartesian components. It consists of two parts: the first, called the labelling of covariants, and its inverse, called the conversion equations. Transformation of parameters from the first domain state to other states is now reduced to irreducible subspaces whose maximal dimension is three in contrast with higher dimensions of tensor spaces. With this method, we can explicitly calculate tensor parameters for all domain states. To find the distinction of pairs of domain states, it is suitable to use the concept of the twinning group which is briefly described. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Kopský, V. 2006-03-01 doi:10.1107/S010876730600078X International Union of Crystallography Tensor parameters of domain states in ferroic phase transitions are considered. It is shown how to find both primary and secondary parameters from the decomposition of tensors into covariants. en DOMAIN STRUCTURES; TENSOR CALCULUS The theory of domain states is reviewed as a prerequisite for consideration of tensorial distinction of domain states. It is then shown that the parameters of the first domain in a ferroic phase transition from a set of isomorphic groups of the same oriented Laue class can be systematically and suitably represented in terms of typical variables. On replacing these variables by actual tensor components according to the previous paper [Kopský (2006), Acta Cryst. A62, 47–64], we can reveal the tensorial parameters associated with each particular symmetry descent. Parameters are distinguished by the ireps to which they belong and this can be used to determine which of them are the principal parameters that distinguish all domain states, in contrast to secondary parameters which are common to several domain states. In general, the parameters are expressed as the covariant components of the tensors. A general procedure is described which is designed to transform the results to Cartesian components. It consists of two parts: the first, called the labelling of covariants, and its inverse, called the conversion equations. Transformation of parameters from the first domain state to other states is now reduced to irreducible subspaces whose maximal dimension is three in contrast with higher dimensions of tensor spaces. With this method, we can explicitly calculate tensor parameters for all domain states. To find the distinction of pairs of domain states, it is suitable to use the concept of the twinning group which is briefly described. text/html Application of modern tensor calculus to engineered domain structures. 2. Tensor distinction of domain states text 2 62 2006-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 feature articles 65 med@iucr.org 76 1600-5724 http://scripts.iucr.org/cgi-bin/paper?xo5007 This article is a roadmap to a systematic calculation and tabulation of tensorial covariants for the point groups of material physics. The following are the essential steps in the described approach to tensor calculus. (i) An exact specification of the considered point groups by their embellished Hermann–Mauguin and Schoenflies symbols. (ii) Introduction of oriented Laue classes of magnetic point groups. (iii) An exact specification of matrix ireps (irreducible representations). (iv) Introduction of so-called typical (standard) bases and variables – typical invariants, relative invariants or components of the typical covariants. (v) Introduction of Clebsch–Gordan products of the typical variables. (vi) Calculation of tensorial covariants of ascending ranks with consecutive use of tables of Clebsch–Gordan products. (vii) Opechowski's magic relations between tensorial decompositions. These steps are illustrated for groups of the tetragonal oriented Laue class D4z − 4z2x2xy of magnetic point groups and for tensors up to fourth rank. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Kopský, V. 2006-03-01 doi:10.1107/S0108767306000778 International Union of Crystallography A systematic approach to calculation of the decomposition of material tensors, including magnetic properties, into tensorial covariants is described. en DOMAIN STRUCTURES; TENSOR CALCULUS This article is a roadmap to a systematic calculation and tabulation of tensorial covariants for the point groups of material physics. The following are the essential steps in the described approach to tensor calculus. (i) An exact specification of the considered point groups by their embellished Hermann–Mauguin and Schoenflies symbols. (ii) Introduction of oriented Laue classes of magnetic point groups. (iii) An exact specification of matrix ireps (irreducible representations). (iv) Introduction of so-called typical (standard) bases and variables – typical invariants, relative invariants or components of the typical covariants. (v) Introduction of Clebsch–Gordan products of the typical variables. (vi) Calculation of tensorial covariants of ascending ranks with consecutive use of tables of Clebsch–Gordan products. (vii) Opechowski's magic relations between tensorial decompositions. These steps are illustrated for groups of the tetragonal oriented Laue class D4z − 4z2x2xy of magnetic point groups and for tensors up to fourth rank. text/html Application of modern tensor calculus to engineered domain structures. 1. Calculation of tensorial covariants text 2 62 2006-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 feature articles 47 med@iucr.org 64 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pz5027 Daughter crystals in orientation relationship with a parent crystal are called variants. They can be created by a structural phase transition (Landau or reconstructive), by twinning or by precipitation. Internal and external classes of transformations defined from the point groups of the parent and daughter phases and from a transformation matrix allow the orientations of the distinct variants to be determined. These are algebraically identified with left cosets and their number is given by the Lagrange formula. A simple equation links the numbers of variants of the direct and inverse transitions. The equivalence classes on the transformations between variants are isomorphic to the double cosets (operators) and their number is given by the Burnside formula. The orientational variants and the operators constitute a groupoid whose composition table acts as a crystallographic signature of the transition. A general method that determines if two daughter variants can be inherited from more than one parent crystal is also described. A computer program has been written to calculate all these properties for any structural transition; some results are given for Burgers transitions and for martensitic transitions in steels. The complexity, irreversibility and entropy of fractal systems constituted by orientational variants generated by thermal cycling are briefly discussed. Copyright (c) 2006 International Union of Crystallography urn:issn:0108-7673 Cayron, C. 2006-01-01 doi:10.1107/S010876730503686X International Union of Crystallography The orientational variants generated by twinning, precipitation or phase transition are algebraically described by a groupoid theory. en COSET; GROUPOID; ORIENTATION; PHASE TRANSITION; SYMMETRY; VARIANT Daughter crystals in orientation relationship with a parent crystal are called variants. They can be created by a structural phase transition (Landau or reconstructive), by twinning or by precipitation. Internal and external classes of transformations defined from the point groups of the parent and daughter phases and from a transformation matrix allow the orientations of the distinct variants to be determined. These are algebraically identified with left cosets and their number is given by the Lagrange formula. A simple equation links the numbers of variants of the direct and inverse transitions. The equivalence classes on the transformations between variants are isomorphic to the double cosets (operators) and their number is given by the Burnside formula. The orientational variants and the operators constitute a groupoid whose composition table acts as a crystallographic signature of the transition. A general method that determines if two daughter variants can be inherited from more than one parent crystal is also described. A computer program has been written to calculate all these properties for any structural transition; some results are given for Burgers transitions and for martensitic transitions in steels. The complexity, irreversibility and entropy of fractal systems constituted by orientational variants generated by thermal cycling are briefly discussed. text/html Groupoid of orientational variants text 1 62 2006-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2006 International Union of Crystallography 0108-7673 research papers 21 med@iucr.org 40 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh5034 The purpose of this paper and a test case study is to assess a method of ab initio structure solution from powder diffraction data using f′ difference techniques. A theoretical foundation for the approach used is first provided. Then, with a test case (nickel sulfate hexahydrate), it is shown that both the position of the anomalous scatterer (Ni) can be determined and the structure can be developed in full. Specifically, synchrotron-radiation data were collected at two wavelengths close to the K edge for Ni and three wavelengths remote from the Ni absorption edge, at 1.3, 1.8 and 2.16 Å. These five wavelengths then allowed various combinations to be tried to establish which wavelength pairs gave the optimum signal in the Patterson maps using dispersive amplitude differences. The initial phases derived from the metal-atom position then allowed the structure to be fully developed by difference Fourier cycling. The relevance of these developments to structure-solution possibilities for proteins via powder dispersive difference data is then outlined. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Helliwell, J.R. Helliwell, M. Jones, R.H. 2005-11-01 doi:10.1107/S010876730503237X International Union of Crystallography A theoretical foundation and test-case evaluation is presented for de novo structure determination using f′ difference techniques. Prospects for extension of these methods to larger molecules than are currently tackled, including proteins, and the possible use of softer X-rays are discussed. en ANOMALOUS SCATTERING; POWDER DIFFRACTION; PROTEIN MICROCRYSTALS; SYNCHROTRON RADIATION The purpose of this paper and a test case study is to assess a method of ab initio structure solution from powder diffraction data using f′ difference techniques. A theoretical foundation for the approach used is first provided. Then, with a test case (nickel sulfate hexahydrate), it is shown that both the position of the anomalous scatterer (Ni) can be determined and the structure can be developed in full. Specifically, synchrotron-radiation data were collected at two wavelengths close to the K edge for Ni and three wavelengths remote from the Ni absorption edge, at 1.3, 1.8 and 2.16 Å. These five wavelengths then allowed various combinations to be tried to establish which wavelength pairs gave the optimum signal in the Patterson maps using dispersive amplitude differences. The initial phases derived from the metal-atom position then allowed the structure to be fully developed by difference Fourier cycling. The relevance of these developments to structure-solution possibilities for proteins via powder dispersive difference data is then outlined. text/html Ab initio structure determination using dispersive differences from multiple-wavelength synchrotron-radiation powder diffraction data text 6 61 2005-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 research papers 568 med@iucr.org 574 1600-5724 http://scripts.iucr.org/cgi-bin/paper?me0302 The proposed crystalline phase identifier consists of a number of components (layers) describing enough properties of the phase to allow a unique identification. These layers consist of the chemical formula, a flag indicating the state of matter, the space-group number and the Wyckoff sequence. They are defined in such a way that they can be incorporated into the IUPAC International Chemical Identifier (InChI) proposed by the International Union of Pure and Applied Chemistry (IUPAC). Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Brown, I.D. Abrahams, S.C. Berndt, M. Faber, J. Karen, V.L. Motherwell, W.D.S. Villars, P. Westbrook, J.D. McMahon, B. 2005-11-01 doi:10.1107/S010876730503179X International Union of Crystallography The proposed crystalline phase identifier consists of a number of components (layers) describing enough properties of the phase to allow a unique identification. These layers consist of the chemical formula, a flag indicating the state of matter, the space-group number and the Wyckoff sequence. They are defined in such a way that they can be incorporated into the IUPAC International Chemical Identifier (InChI) proposed by the International Union of Pure and Applied Chemistry (IUPAC). en CRYSTAL PHASE IDENTIFIERS; NOMENCLATURE The proposed crystalline phase identifier consists of a number of components (layers) describing enough properties of the phase to allow a unique identification. These layers consist of the chemical formula, a flag indicating the state of matter, the space-group number and the Wyckoff sequence. They are defined in such a way that they can be incorporated into the IUPAC International Chemical Identifier (InChI) proposed by the International Union of Pure and Applied Chemistry (IUPAC). text/html Report of the Working Group on Crystal Phase Identifiers text 6 61 2005-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 research papers 575 med@iucr.org 580 1600-5724 http://scripts.iucr.org/cgi-bin/paper?gc0052 The efficacy of direct methods for solving the crystal structures of zeolites from electron diffraction data is evaluated for a series of related materials, i.e. MCM-22, MCM-49 and ITQ-1. First, it is established by tilting experiments that all materials share the same MWW framework. The calcined product of a delaminated MCM-22 precursor, ITQ-2, also shares this framework structure within the limited number of stacked unit cells. For all materials, the underlying space group is P6/mmm where a ≃ 14.21, c ≃ 24.94 Å. Traditional direct methods are useful for determining the projected structure down the hexagonal axis but are not very effective for finding the three-dimensional structure. On the other hand, maximum-entropy and likelihood approaches are effective for determining either 2D projections or 3D frameworks. The major restriction to 3D determinations by direct methods is the limited goniometric tilt range of the electron microscope, hence the `missing cone' of information. Potential maps from the most accurate phase sets are, therefore, observed as continuous density envelopes to the true structure. Some improvement is found when the Sayre equation predicts missing amplitudes and phases but it is clear that better specimen preparation methods are required to include projections containing the c∗ axis of the reciprocal lattice. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Dorset, D.L. Roth, W.J. Gilmore, C.J. 2005-09-01 doi:10.1107/S0108767305024670 International Union of Crystallography The 3D crystal structure of zeolites in the MWW framework family is determined from electron diffraction intensities by direct phasing using maximum entropy and likelihood. Although the `missing cone' left from incomplete goniometric data sampling leads to a somewhat distorted model, the true zeolite framework geometry may be recovered by imposing conservative bonding restraints. en ELECTRON CRYSTALLOGRAPHY; ZEOLITES The efficacy of direct methods for solving the crystal structures of zeolites from electron diffraction data is evaluated for a series of related materials, i.e. MCM-22, MCM-49 and ITQ-1. First, it is established by tilting experiments that all materials share the same MWW framework. The calcined product of a delaminated MCM-22 precursor, ITQ-2, also shares this framework structure within the limited number of stacked unit cells. For all materials, the underlying space group is P6/mmm where a ≃ 14.21, c ≃ 24.94 Å. Traditional direct methods are useful for determining the projected structure down the hexagonal axis but are not very effective for finding the three-dimensional structure. On the other hand, maximum-entropy and likelihood approaches are effective for determining either 2D projections or 3D frameworks. The major restriction to 3D determinations by direct methods is the limited goniometric tilt range of the electron microscope, hence the `missing cone' of information. Potential maps from the most accurate phase sets are, therefore, observed as continuous density envelopes to the true structure. Some improvement is found when the Sayre equation predicts missing amplitudes and phases but it is clear that better specimen preparation methods are required to include projections containing the c∗ axis of the reciprocal lattice. text/html Electron crystallography of zeolites – the MWW family as a test of direct 3D structure determination text 5 61 2005-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 research papers 516 med@iucr.org 527 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh0182 Symmetry and physical aspects of `forbidden' reflections excited by a local polarization anisotropy of the X-ray susceptibility are surveyed. Such reflections are observed near absorption edges where the anisotropy is caused by distortions of the atomic electronic states owing to interaction with neighbouring atoms. As a consequence, they allow for extracting nontrivial information about the resonant atom's local environment and their physical conditions. The unusual polarization properties of the considered reflections are helpful to distinguish them from other types of `forbidden' reflections. When such reflections are excited, it is, for example, possible to determine not only the intrinsic anisotropy of an atomic form factor but also additional anisotropy induced by thermal motion, point defects and/or incommensurate modulations. Even the local `chirality' of atoms in centrosymmetric crystals is accessible. Unsolved key problems and possible future developments are addressed. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Dmitrienko, V.E. Ishida, K. Kirfel, A. Ovchinnikova, E.N. 2005-09-01 doi:10.1107/S0108767305018209 International Union of Crystallography In the resonant region near an absorption edge, a polarization anisotropy of the local X-ray susceptibility results in additional reflections otherwise forbidden by screw-axis and/or glide-plane extinction rules. en FORBIDDEN REFLECTIONS; RESONANT X-RAY DIFFRACTION; X-RAY ANISOTROPY Symmetry and physical aspects of `forbidden' reflections excited by a local polarization anisotropy of the X-ray susceptibility are surveyed. Such reflections are observed near absorption edges where the anisotropy is caused by distortions of the atomic electronic states owing to interaction with neighbouring atoms. As a consequence, they allow for extracting nontrivial information about the resonant atom's local environment and their physical conditions. The unusual polarization properties of the considered reflections are helpful to distinguish them from other types of `forbidden' reflections. When such reflections are excited, it is, for example, possible to determine not only the intrinsic anisotropy of an atomic form factor but also additional anisotropy induced by thermal motion, point defects and/or incommensurate modulations. Even the local `chirality' of atoms in centrosymmetric crystals is accessible. Unsolved key problems and possible future developments are addressed. text/html Polarization anisotropy of X-ray atomic factors and `forbidden' resonant reflections text 5 61 2005-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 topical reviews 481 med@iucr.org 493 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh5029 A common measure of conformational similarity in structural bioinformatics is the minimum root mean square deviation (RMSD) between the coordinates of two macromolecules. In many applications, the rotations relating the structures are not needed. Several common algorithms for calculating RMSDs require the computationally costly procedures of determining either the eigen decomposition or matrix inversion of a 3\times3 or 4\times4 matrix. Using a quaternion-based method, here a simple algorithm is developed that rapidly and stably determines RMSDs by circumventing the decomposition and inversion problems. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Theobald, D.L. 2005-07-01 doi:10.1107/S0108767305015266 International Union of Crystallography Using a quaternion-based characteristic polynomial, a simple algorithm is developed that rapidly and stably determines root mean square deviations for structural superpositions. en CHARACTERISTIC EQUATION; QUARTIC POLYNOMIAL; QUATERNION; RMSD; SUPERPOSITION A common measure of conformational similarity in structural bioinformatics is the minimum root mean square deviation (RMSD) between the coordinates of two macromolecules. In many applications, the rotations relating the structures are not needed. Several common algorithms for calculating RMSDs require the computationally costly procedures of determining either the eigen decomposition or matrix inversion of a 3\times3 or 4\times4 matrix. Using a quaternion-based method, here a simple algorithm is developed that rapidly and stably determines RMSDs by circumventing the decomposition and inversion problems. text/html Rapid calculation of RMSDs using a quaternion-based characteristic polynomial text 4 61 2005-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 short communications 478 med@iucr.org 480 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0014 Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Durovič, S. 2005-09-01 doi:10.1107/S0108767305004307 International Union of Crystallography en BOOK REVIEW text/html Crystallography of modular materials. By Giovanni Ferraris, Emil Makovicky and Stefano Merlino. Pp. x + 370. Oxford: Oxford University Press, 2004. Price Hardback GBP 75.00. ISBN 0-19-852664-4. text 5 61 2005-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 book reviews 531 med@iucr.org 532 1600-5724 http://scripts.iucr.org/cgi-bin/paper?es0342 Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 2005-03-01 doi:10.1107/S0108767305002345 International Union of Crystallography en text/html Mario Nardelli (1922–2004) text 2 61 2005-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 obituaries 159 med@iucr.org 161 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0009 Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Glusker, J.P. 2005-03-01 doi:10.1107/S0108767305001285 International Union of Crystallography en BOOK REVIEW text/html Crystal structure determination. Second edition. By Werner Massa. Pp. xi + 210. Translated into English by Robert O. Gould. Berlin: Springer, 2004. Price EUR 44.95, USD 49.95. ISBN 3-540-20644-2. text 2 61 2005-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 book reviews 261 med@iucr.org 262 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0015 Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 North, A.C.T. 2005-03-01 doi:10.1107/S0108767305001273 International Union of Crystallography en BOOK REVIEW text/html Light is a messenger – the life and science of William Lawrence Bragg. By G. K. Hunter. Pp. xxi + 301. Oxford: Oxford University Press, 2004. Price Hardback GBP 35.00. ISBN 0-19-852921-X. text 2 61 2005-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 book reviews 262 med@iucr.org 264 1600-5724 http://scripts.iucr.org/cgi-bin/paper?me0287 Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Pandey, D. 2005-01-01 doi:10.1107/S0108767304033434 International Union of Crystallography en PHASE TRANSITIONS text/html Themed issues of Acta Crystallographica Section A on phase transitions text 1 61 2005-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 topical reviews 1 med@iucr.org 2 1600-5724 http://scripts.iucr.org/cgi-bin/paper?es0338 Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Moodie, A. 2005-01-01 doi:10.1107/S0108767304029484 International Union of Crystallography en OBITUARY text/html John M. Cowley FAA FRS (1923–2004) text 1 61 2005-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 obituaries 122 med@iucr.org 124 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0008 Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Aroyo, M. 2005-03-01 doi:10.1107/S0108767304029186 International Union of Crystallography en BOOK REVIEW text/html Mathematical techniques in crystallog­raphy and materials science. Third edition. By Edward Prince. Pp. vii + 224. Berlin and Heidelberg: Springer-Verlag, 2004. Price EUR 39.95 (soft cover). ISBN 3-540-21111-X. text 2 61 2005-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 book reviews 260 med@iucr.org 261 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf5001 Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Paufler, P.P. 2005-03-01 doi:10.1107/S0108767304028569 International Union of Crystallography en BOOK RECEIVED text/html X-ray Compton scattering. By Malcolm J. Cooper, Peter E. Mijnarends, Nobuhiro Shiotani, Nobuhiko Sakai and Arun Bansil. Oxford: Oxford University Press, 2004, pp. XVII + 374. Price GPB 95.10. ISBN 0 19 850168 4. text 2 61 2005-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 books received 264 med@iucr.org 264 1600-5724 http://scripts.iucr.org/cgi-bin/paper?mm5009 A direct method for determining powder diffraction data at specific depths from angle-dependent diffraction data is described. The method is non-destructive and only traditional data collections, where the angle of incidence is varied, are required. These angle-dependent spectra are transformed to give diffraction data arising from different depths, which may then be exploited using any conventional method. This is a novel approach as traditional methods are forced to tolerate the inherent depth averaging of grazing-angle diffraction, or only examine specific structural characteristics. In order to obtain depth-dependent X-ray diffraction data, a Fredholm integral equation of the first kind is solved using regularization techniques. The method has been validated by the generation of pseudo-experimental data having known depth profiles and solving the Fredholm integral equation to recover the solution. The method has also been applied to experimental data from a number of thin film systems. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Broadhurst, A. Rogers, K.D. Lowe, T.W. Lane, D.W. 2005-01-01 doi:10.1107/S0108767304026881 International Union of Crystallography A direct method for transforming angle-dependent diffraction data into depth-dependent data by the use of regularization techniques is presented, including method validation and application to experimental data. en DEPTH PROFILING; FREDHOLM INTEGRAL EQUATION; REGULARIZATION A direct method for determining powder diffraction data at specific depths from angle-dependent diffraction data is described. The method is non-destructive and only traditional data collections, where the angle of incidence is varied, are required. These angle-dependent spectra are transformed to give diffraction data arising from different depths, which may then be exploited using any conventional method. This is a novel approach as traditional methods are forced to tolerate the inherent depth averaging of grazing-angle diffraction, or only examine specific structural characteristics. In order to obtain depth-dependent X-ray diffraction data, a Fredholm integral equation of the first kind is solved using regularization techniques. The method has been validated by the generation of pseudo-experimental data having known depth profiles and solving the Fredholm integral equation to recover the solution. The method has also been applied to experimental data from a number of thin film systems. text/html Determination of depth-dependent diffraction data: a new approach text 1 61 2005-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 research papers 139 med@iucr.org 146 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pd5027 A short review is given of recent X-ray diffraction studies of the phases and phase transitions of thermotropic liquid crystals. The areas covered are twist-grain-boundary phases, antiferroelectric phases studied with resonant X-ray diffraction and smectic phases within gel structures. In all areas, X-ray diffraction has played a key role. Nonetheless, open questions remain: the nature of the smectic C variant of the twist-grain-boundary phase, the origin of antiferroelectric phases, and whether novel Bragg glass states exist for smectic A gel samples. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Clegg, P.S. 2005-01-01 doi:10.1107/S0108767304025991 International Union of Crystallography Recent X-ray diffraction studies of liquid crystals are reviewed. The topics are twist grain-boundary phases, antiferroelectric phases studied using resonant diffraction and smectic phases within gel structures. en LIQUID CRYSTALS; PHASE TRANSITIONS A short review is given of recent X-ray diffraction studies of the phases and phase transitions of thermotropic liquid crystals. The areas covered are twist-grain-boundary phases, antiferroelectric phases studied with resonant X-ray diffraction and smectic phases within gel structures. In all areas, X-ray diffraction has played a key role. Nonetheless, open questions remain: the nature of the smectic C variant of the twist-grain-boundary phase, the origin of antiferroelectric phases, and whether novel Bragg glass states exist for smectic A gel samples. text/html X-ray studies of the phases and phase transitions of liquid crystals text 1 61 2005-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 topical reviews 112 med@iucr.org 121 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0003 Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Paufler, P.P. 2004-11-01 doi:10.1107/S0108767304021701 International Union of Crystallography en text/html Crystal structure determination. By Werner Massa. Second completely updated edition. Pp. XI + 210. Berlin, Heidelberg, New York: Springer-Verlag, 2004. Price EUR 48.10. ISBN 3 540 20644 2. text 6 60 2004-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 books received 642 med@iucr.org 642 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0002 Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Paufler, P.P. 2004-11-01 doi:10.1107/S0108767304021695 International Union of Crystallography en text/html Orientations and rotations. Computations in crystallographic textures. By Adam Morawiec. Pp. X + 200. Berlin, Heidelberg, New York: Springer-Verlag, 2004. Price EUR 59.95, GBP 46.00, USD 79.95. ISBN 3 540 40734 0. text 6 60 2004-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 books received 642 med@iucr.org 642 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0007 Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Paufler, P.P. 2004-11-01 doi:10.1107/S0108767304021713 International Union of Crystallography en text/html Mathematical techniques in crystallog­raphy and materials science. By Edward Prince. 3rd ed. Pp. XI + 224. Berlin, Heidelberg, New York: Springer-Verlag, 2004. Price (softcover) EUR 42.75. ISBN 3 540 21111 X. text 6 60 2004-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 books received 642 med@iucr.org 642 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pd5028 An overview is presented of low-dimensional electronic crystals that undergo a phase transition towards a low-temperature charge-density-wave (CDW) state. The emphasis is on inorganic compounds that develop an one-dimensional (1D) CDW. Low-dimensional features of crystal structures are discussed in relation to 1D electronic properties. X-ray diffraction is discussed as a tool to obtain quantitative information about the normal state and its structural fluctuations, and about the CDW, both in equilibrium and in its non-linear conducting state. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Smaalen, S. van 2005-01-01 doi:10.1107/S0108767304025437 International Union of Crystallography An overview is presented of inorganic compounds with low-dimensional electronic structures, and of X-ray diffraction as a tool to study the properties of charge-density waves (CDWs). en ELECTRONIC CRYSTALS; PEIERLS TRANSITION; PHASE TRANSITIONS An overview is presented of low-dimensional electronic crystals that undergo a phase transition towards a low-temperature charge-density-wave (CDW) state. The emphasis is on inorganic compounds that develop an one-dimensional (1D) CDW. Low-dimensional features of crystal structures are discussed in relation to 1D electronic properties. X-ray diffraction is discussed as a tool to obtain quantitative information about the normal state and its structural fluctuations, and about the CDW, both in equilibrium and in its non-linear conducting state. text/html The Peierls transition in low-dimensional electronic crystals text 1 61 2005-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 topical reviews 51 med@iucr.org 61 1600-5724 http://scripts.iucr.org/cgi-bin/paper?sh0180 In the paper `A strict solution for the optimal superimposition of protein structures' by Chuanbo Chen & Qishen Li [Acta Cryst. (2004), A60, 201–203], we claimed that existing methods for the optimal superimposition of two point sets, requiring the precondition of coincident centroids, are mathematically not strict. It has been brought to our attention that this claim is erroneous. We therefore retract the publication. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Chen, C. Li, Q. 2004-11-01 doi:10.1107/S0108767304024730 International Union of Crystallography The manuscript that appeared in Acta Cryst. (2004), A60, 201–203 is retracted. en BIOINFORMATICS; PROTEIN STRUCTURE; OPTIMAL SUPERIMPOSITION In the paper `A strict solution for the optimal superimposition of protein structures' by Chuanbo Chen & Qishen Li [Acta Cryst. (2004), A60, 201–203], we claimed that existing methods for the optimal superimposition of two point sets, requiring the precondition of coincident centroids, are mathematically not strict. It has been brought to our attention that this claim is erroneous. We therefore retract the publication. text/html A strict solution for the optimal superimposition of protein structures. Retraction text 6 60 2004-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 addenda and errata 640 med@iucr.org 640 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pf0012 Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Paufler, P. 2004-11-01 doi:10.1107/S0108767304022536 International Union of Crystallography en BOOK REVIEWS text/html International tables for crystallography. Vol. A. 5th edition. Edited by Th. Hahn. Pp. xx + 911. Dordrecht: Kluwer Academic Publishers, 2002. Price EUR 242, GBP 142, USD 225. ISBN 0-7923-6590-9. text 6 60 2004-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 book reviews 641 med@iucr.org 642 1600-5724 http://scripts.iucr.org/cgi-bin/paper?pd5021 Landau-type theories describe the observed behaviour of phase transitions in ferroelastic and co-elastic minerals and materials with a high degree of accuracy. In this review, the derivation of the Landau potential G = ½AθS [coth(θS/T) − coth(θS/TC)]Q2 + ¼BQ4 + … is derived as a solution of the general φ4 model. The coupling between the order parameter and spontaneous strain of a phase transition brings the behaviour of many phase transitions to the mean-field limit, even when the atomistic mechanism of the transition is spin-like. Strain coupling is also a common mechanism for the coupling between multiple order parameters in a single system. As well as changes on the crystal structure scale, phase transitions modify the microstructure of materials, leading to anomalous mesoscopic features at domain boundaries. The mesostructure of a domain wall is studied experimentally using X-ray diffraction, and interpreted theoretically using Ginzburg–Landau theory. One important consequence of twin meso­structures is their modified transport properties relative to the bulk. Domain wall motion also provides a mechanism for superelastic behaviour in ferroelastics. At surfaces, the relaxations that occur can be described in terms of order parameters and Landau theory. This leads to an exponential profile of surface relaxations. This in turn leads to an exponential interaction energy between surfaces, which can, if large enough, destabilize symmetrical morphologies in favour of a platelet morphology. Surface relaxations may also affect the behaviour of twin walls as they intersect surfaces, since the surface relaxation may lead to an incompatibility of the two domains at the surface, generating large strains at the relaxation. Landau theory may also be extended to describe the kinetics of phase transitions. Time-dependent Landau theory may be used to describe the kinetics of order–disorder phase transitions in which the order parameter is homogeneous. However, the time-dependent Landau theory equations also have microstructural solutions, explaining the formation of microstructures such as tweed. Copyright (c) 2005 International Union of Crystallography urn:issn:0108-7673 Salje, E.K.H. Hayward, S.A. Lee, W.T. 2005-01-01 doi:10.1107/S0108767304020318 International Union of Crystallography The uses of Landau-type theories to describe structural, microstructural and mesostructural features of materials undergoing phase transitions are reviewed. en ANORTHITE; KINETICS; LANDAU THEORY; MESOSTRUCTURE; OMPHACITE; PHASE TRANSITIONS; STRAIN COUPLING; SUPERELASTICITY; SURFACE RELAXATION Landau-type theories describe the observed behaviour of phase transitions in ferroelastic and co-elastic minerals and materials with a high degree of accuracy. In this review, the derivation of the Landau potential G = ½AθS [coth(θS/T) − coth(θS/TC)]Q2 + ¼BQ4 + … is derived as a solution of the general φ4 model. The coupling between the order parameter and spontaneous strain of a phase transition brings the behaviour of many phase transitions to the mean-field limit, even when the atomistic mechanism of the transition is spin-like. Strain coupling is also a common mechanism for the coupling between multiple order parameters in a single system. As well as changes on the crystal structure scale, phase transitions modify the microstructure of materials, leading to anomalous mesoscopic features at domain boundaries. The mesostructure of a domain wall is studied experimentally using X-ray diffraction, and interpreted theoretically using Ginzburg–Landau theory. One important consequence of twin meso­structures is their modified transport properties relative to the bulk. Domain wall motion also provides a mechanism for superelastic behaviour in ferroelastics. At surfaces, the relaxations that occur can be described in terms of order parameters and Landau theory. This leads to an exponential profile of surface relaxations. This in turn leads to an exponential interaction energy between surfaces, which can, if large enough, destabilize symmetrical morphologies in favour of a platelet morphology. Surface relaxations may also affect the behaviour of twin walls as they intersect surfaces, since the surface relaxation may lead to an incompatibility of the two domains at the surface, generating large strains at the relaxation. Landau theory may also be extended to describe the kinetics of phase transitions. Time-dependent Landau theory may be used to describe the kinetics of order–disorder phase transitions in which the order parameter is homogeneous. However, the time-dependent Landau theory equations also have microstructural solutions, explaining the formation of microstructures such as tweed. text/html Ferroelastic phase transitions: structure and microstructure text 1 61 2005-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2005 International Union of Crystallography 0108-7673 topical reviews 3 med@iucr.org 18 1600-5724 http://scripts.iucr.org/cgi-bin/paper?me0264 Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Larsen, F.K. 2004-09-01 doi:10.1107/S010876730402032X International Union of Crystallography en PREFACE; CHARGE DENSITY text/html New information from modern charge density methods text 5 60 2004-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 issue preface med@iucr.org http://scripts.iucr.org/cgi-bin/paper?xc5020 Over the past decade, there has been much development in the structure determination of photoinduced species by single-crystal X-ray diffraction. Such work is key to understanding many photoactivated chemical processes and physical properties that are behind phenomena such as photoisomerism, photoinduced chemical reactions, light-induced spin-crossover transitions and molecular excited states that are responsible for many types of fluorescence and phosphorescence. A brief overview of these experimental developments is presented in relation to the attraction of conducting charge-density studies on photoinduced structures. The technical issues regarding possible charge-density studies using these developments, both in the metastable and time-resolved domain, are highlighted in the form of a perspective towards future possibilities for photoinduced charge-density studies. The paper concludes with a summary of further experimental developments that are unfolding and how these may contribute to the ultimate viability of `in-situ' charge-density studies on photoinduced phenomena. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Cole, J.M. 2004-09-01 doi:10.1107/S0108767304017428 International Union of Crystallography The experimental considerations required to obtain photoinduced crystal structures is described and related to the experimental and theoretical requirements of charge-density studies. The viability of combining these two experimental methodologies to realize a photoinduced charge-density study is explored. en CHARGE DENSITY; PHOTOINDUCED PHENOMENA Over the past decade, there has been much development in the structure determination of photoinduced species by single-crystal X-ray diffraction. Such work is key to understanding many photoactivated chemical processes and physical properties that are behind phenomena such as photoisomerism, photoinduced chemical reactions, light-induced spin-crossover transitions and molecular excited states that are responsible for many types of fluorescence and phosphorescence. A brief overview of these experimental developments is presented in relation to the attraction of conducting charge-density studies on photoinduced structures. The technical issues regarding possible charge-density studies using these developments, both in the metastable and time-resolved domain, are highlighted in the form of a perspective towards future possibilities for photoinduced charge-density studies. The paper concludes with a summary of further experimental developments that are unfolding and how these may contribute to the ultimate viability of `in-situ' charge-density studies on photoinduced phenomena. text/html `In-situ' charge-density studies of photoinduced phenomena: possibilities for the future? text 5 60 2004-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 research papers 472 med@iucr.org 479 http://scripts.iucr.org/cgi-bin/paper?gc0049 A review of 4 × 4-matrix notation and of tensor formalism focused on crystallographic applications is presented. A discussion of examples shows how this notation simplifies tasks encountered in crystallographic computing. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Rowicka, M. Kudlicki, A. Zelinka, J. Otwinowski, Z. 2004-11-01 doi:10.1107/S0108767304017398 International Union of Crystallography A review of 4 × 4 matrix notation and of tensor formalism focused on crystallographic applications, including examples from crystallographic computing. en MATRIX NOTATION; TENSOR FORMALISM; COORDINATE TRANSFORMATIONS A review of 4 × 4-matrix notation and of tensor formalism focused on crystallographic applications is presented. A discussion of examples shows how this notation simplifies tasks encountered in crystallographic computing. text/html Coordinate transformations in modern crystallographic computing text 6 60 2004-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 research papers 542 med@iucr.org 549 1600-5724 http://scripts.iucr.org/cgi-bin/paper?xc5015 The electrostatic potential can be used as an appropriate and convenient indicator of how transferable an atom or functional group is between two molecules. Quantum-chemical topology (QCT) is used to define the electron density of a molecular fragment and the electrostatic potential it generates. The potential generated on a grid by the terminal aldehyde group of the biomolecule retinal is compared with the corresponding aldehyde group in smaller molecules derived from retinal. The terminal amino group in the free amino acid lysine was treated in a similar fashion. Each molecule is geometry-optimized by an ab initio calculation at B3LYP/6-311G+(2d,p)//HF/6-31G(d) level. The amino group in lysine is very little influenced by any part of the molecule further than two C atoms away. However, the aldehyde group in retinal is influenced by molecular fragments six C atoms away. This dramatic disparity is ascribed to the difference in saturation in the carbon chains; retinal contains a conjugated hydrocarbon chain but lysine an aliphatic one. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Popelier, P.L.A. Devereux, M. Rafat, M. 2004-09-01 doi:10.1107/S0108767304016228 International Union of Crystallography The electrostatic potential can be used as an appropriate and convenient indicator of how transferable an atom or functional group is between two molecules. Quantum-chemical topology is used to define the electron density of a molecular fragment and the electrostatic potential it generates. en ELECTRON DENSITY; QUANTUM-CHEMICAL TOPOLOGY; ELECTROSTATIC POTENTIAL; FUNCTIONAL GROUP TRANSFERABILITY The electrostatic potential can be used as an appropriate and convenient indicator of how transferable an atom or functional group is between two molecules. Quantum-chemical topology (QCT) is used to define the electron density of a molecular fragment and the electrostatic potential it generates. The potential generated on a grid by the terminal aldehyde group of the biomolecule retinal is compared with the corresponding aldehyde group in smaller molecules derived from retinal. The terminal amino group in the free amino acid lysine was treated in a similar fashion. Each molecule is geometry-optimized by an ab initio calculation at B3LYP/6-311G+(2d,p)//HF/6-31G(d) level. The amino group in lysine is very little influenced by any part of the molecule further than two C atoms away. However, the aldehyde group in retinal is influenced by molecular fragments six C atoms away. This dramatic disparity is ascribed to the difference in saturation in the carbon chains; retinal contains a conjugated hydrocarbon chain but lysine an aliphatic one. text/html The quantum topological electrostatic potential as a probe for functional group transferability text 5 60 2004-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 research papers 427 med@iucr.org 433 http://scripts.iucr.org/cgi-bin/paper?sh0179 Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Volkov, A. Koritsanszky, T. Li, X. Coppens, P. 2004-11-01 doi:10.1107/S0108767304016496 International Union of Crystallography Comment on Pichon-Pesme et al. [Acta Cryst. (2004), A60, 204–208]. en CHARGE DENSITY; ELECTRON DENSITY; POLYPEPTIDES; MACROMOLECULAR CRYSTALLOGRAPHY; PROTEIN CRYSTALLOGRAPHY; DATABASE text/html Response to the paper A comparison between experimental and theoretical aspherical-atom scattering factors for charge-density refinement of large molecules, by Pichon-Pesme, Jelsch, Guillot & Lecomte (2004) text 6 60 2004-11-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 letters to the editor 638 med@iucr.org 639 1600-5724 http://scripts.iucr.org/cgi-bin/paper?xc5014 High-resolution X-ray diffraction data were collected at T = 19 K from two similar spherical crystals of the fungal metabolite citrinin, C13H14O5. The two data sets were of markedly different quality, one data set (MQ, medium quality) comprising a single octant of the reciprocal lattice and including reflections with obviously peculiar intensity profiles while the second (HQ, high quality) comprised a hemisphere of reflections and showed no flawed profiles. Parallel multipolar refinements were carried out for both. While most of the resulting geometric parameters, including bond lengths and angles, were in close agreement (the standard uncertainties were approximately twice as large for the MQ data, reflecting the smaller number of observations), the agreement is noticeably worse for electronic properties such as electron densities and their Laplacians at the bond and ring critical points. These latter features are especially sensitive to the quality of the low-angle (and strong) intensities, which was not high for the MQ data. By contrast, the magnitudes of the molecular dipole moment from the two experiments are the same within 1 standard uncertainty, with an angle of about 13° between the two vectors. It is concluded that only true high-quality data allow a fully significant and quantitative analysis of the details of the experimental electron density ρexp, while high-resolution medium-quality data, measured at very low temperature and adequately processed, can still be used for a qualitative analysis, or for the derivation of overall electronic properties. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Destro, R. Loconte, L. Lo Presti, L. Roversi, P. Soave, R. 2004-09-01 doi:10.1107/S0108767304014813 International Union of Crystallography Electron distributions from multipolar refinement of two sets of high-resolution X-ray diffraction data of different quality, measured at T = 19 K from two different spherical crystals of the same compound, are analysed and compared. en ELECTRON DENSITY; TOPOLOGICAL ANALYSIS; MOLECULAR ELECTRIC MOMENTS; DATA QUALITY High-resolution X-ray diffraction data were collected at T = 19 K from two similar spherical crystals of the fungal metabolite citrinin, C13H14O5. The two data sets were of markedly different quality, one data set (MQ, medium quality) comprising a single octant of the reciprocal lattice and including reflections with obviously peculiar intensity profiles while the second (HQ, high quality) comprised a hemisphere of reflections and showed no flawed profiles. Parallel multipolar refinements were carried out for both. While most of the resulting geometric parameters, including bond lengths and angles, were in close agreement (the standard uncertainties were approximately twice as large for the MQ data, reflecting the smaller number of observations), the agreement is noticeably worse for electronic properties such as electron densities and their Laplacians at the bond and ring critical points. These latter features are especially sensitive to the quality of the low-angle (and strong) intensities, which was not high for the MQ data. By contrast, the magnitudes of the molecular dipole moment from the two experiments are the same within 1 standard uncertainty, with an angle of about 13° between the two vectors. It is concluded that only true high-quality data allow a fully significant and quantitative analysis of the details of the experimental electron density ρexp, while high-resolution medium-quality data, measured at very low temperature and adequately processed, can still be used for a qualitative analysis, or for the derivation of overall electronic properties. text/html On the role of data quality in experimental charge-density studies text 5 60 2004-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 research papers 365 med@iucr.org 370 http://scripts.iucr.org/cgi-bin/paper?lc0065 In U4O9, most of the atoms are in general 48-fold [48(e)] sites of the space group I\bar43d and yet the hkl reflections obey the extinction rules for atoms occupying special 12-fold [12(b)] sites. An explanation is given for this effect, which can be generalized to any space group. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Popa, N.C. Willis, B.T.M. 2004-07-01 doi:10.1107/S0108767304012188 International Union of Crystallography In U4O9, the hkl reflections obey the extinction rules for atoms occupying special 12-fold [12(b) of space group I\bar43d] sites. An explanation is given for this effect, which can be generalized to any space group. en SPECIAL REFLECTION CONDITIONS; URANIUM OXIDE; SYSTEMATIC ABSENCES In U4O9, most of the atoms are in general 48-fold [48(e)] sites of the space group I\bar43d and yet the hkl reflections obey the extinction rules for atoms occupying special 12-fold [12(b)] sites. An explanation is given for this effect, which can be generalized to any space group. text/html U4O9: atoms in general sites giving the hkl extinctions of special sites text 4 60 2004-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 research papers 318 med@iucr.org 321 1600-5724 http://scripts.iucr.org/cgi-bin/paper?lc0066 β-U4O9 is a superlattice structure based on the fluorite arrangement of UO2. The U atoms occupy positions close to those in UO2 and the additional O atoms are accommodated in cuboctahedral clusters of \bar43m symmetry, which are centred on the special 12-fold sites of the cubic space group I\bar43d. The structure has been refined from single-crystal neutron data in accordance with the procedure described in the previous paper [Popa & Willis (2004). Acta Cryst. A60, 318–321]. Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Cooper, R.I. Willis, B.T.M. 2004-07-01 doi:10.1107/S010876730401219X International Union of Crystallography The structure of β-U4O9 has been refined from single-crystal neutron data in the space group I\bar43d taking into account the findings described in the previous paper. en CLUSTERS; URANIUM OXIDE; NEUTRON SCATTERING β-U4O9 is a superlattice structure based on the fluorite arrangement of UO2. The U atoms occupy positions close to those in UO2 and the additional O atoms are accommodated in cuboctahedral clusters of \bar43m symmetry, which are centred on the special 12-fold sites of the cubic space group I\bar43d. The structure has been refined from single-crystal neutron data in accordance with the procedure described in the previous paper [Popa & Willis (2004). Acta Cryst. A60, 318–321]. text/html Refinement of the structure of β-U4O9 text 4 60 2004-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 research papers 322 med@iucr.org 325 1600-5724 http://scripts.iucr.org/cgi-bin/paper?me0246 Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Manninen, S. 2004-03-01 doi:10.1107/S0108767304002788 International Union of Crystallography en QUANTUM CRYSTALLOGRAPHY text/html Quantum Crystallography: Electron Density and Bonding, a Microsymposium text 2 60 2004-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 topical reviews 103 med@iucr.org 103 1600-5724 http://scripts.iucr.org/cgi-bin/paper?es0334 Copyright (c) 2004 International Union of Crystallography urn:issn:0108-7673 Duax, W.L. Larsen, S. 2004-01-01 doi:10.1107/S0108767303028964 International Union of Crystallography en text/html Nominations for the Ewald Prize text 1 60 2004-01-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2004 International Union of Crystallography 0108-7673 international union of crystallography 96 med@iucr.org 96 1600-5724 http://scripts.iucr.org/cgi-bin/paper?lc0060 One of the applications of the maximum-entropy method (MEM) in crystallography is the reconstruction of the electron density from phased structure factors. Here the application of the MEM to incommensurately modulated crystals and incommensurate composite crystals is considered. The MEM is computed directly in superspace, where the electron density in the (3+d)-dimensional unit cell (d > 0) is determined from the scattering data of aperiodic crystals. Periodic crystals (d = 0) are treated as a special case of the general formalism. The use of symmetry in the MEM is discussed and an efficient algorithm is proposed for handling crystal symmetry. The method has been implemented into a computer program BayMEM and applications are presented to the electron density of the periodic crystal NaV2O5 and the electron density of the incommensurate composite crystal (LaS)1.14NbS2. The MEM in superspace is shown to provide a model-independent estimate of the shapes of the modulation functions of incommensurate crystals. The discrete character of the electron density is found to be the major source of error, limiting the accuracy of the reconstructed modulation functions to approximately 10% of the sizes of the pixels. MaxEnt optimization using the Cambridge and Sakata–Sato algorithms are compared. The Cambridge algorithm is found to perform better than the Sakata–Sato algorithm, being faster, always reaching convergence, and leading to more reliable density maps. Nevertheless, the Sakata–Sato algorithm leads to similar density maps, even in cases where it does not reach complete convergence. Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Smaalen, S. van Palatinus, L. Schneider, M. 2003-09-01 doi:10.1107/S010876730301434X International Union of Crystallography The maximum-entropy method (MEM) for the analysis of the electron densities of periodic and aperiodic crystals is critically evaluated. It is shown that the MEM in superspace provides a model-independent reconstruction of the shapes of the modulation functions of incommensurate crystals. en MAXIMUM-ENTROPY METHOD; APERIODIC CRYSTALS; ELECTRON DENSITY One of the applications of the maximum-entropy method (MEM) in crystallography is the reconstruction of the electron density from phased structure factors. Here the application of the MEM to incommensurately modulated crystals and incommensurate composite crystals is considered. The MEM is computed directly in superspace, where the electron density in the (3+d)-dimensional unit cell (d > 0) is determined from the scattering data of aperiodic crystals. Periodic crystals (d = 0) are treated as a special case of the general formalism. The use of symmetry in the MEM is discussed and an efficient algorithm is proposed for handling crystal symmetry. The method has been implemented into a computer program BayMEM and applications are presented to the electron density of the periodic crystal NaV2O5 and the electron density of the incommensurate composite crystal (LaS)1.14NbS2. The MEM in superspace is shown to provide a model-independent estimate of the shapes of the modulation functions of incommensurate crystals. The discrete character of the electron density is found to be the major source of error, limiting the accuracy of the reconstructed modulation functions to approximately 10% of the sizes of the pixels. MaxEnt optimization using the Cambridge and Sakata–Sato algorithms are compared. The Cambridge algorithm is found to perform better than the Sakata–Sato algorithm, being faster, always reaching convergence, and leading to more reliable density maps. Nevertheless, the Sakata–Sato algorithm leads to similar density maps, even in cases where it does not reach complete convergence. text/html The maximum-entropy method in superspace text 5 59 2003-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 research papers 459 med@iucr.org 469 1600-5724 http://scripts.iucr.org/cgi-bin/paper?ht5045 Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Vincent, R. 2003-09-01 doi:10.1107/S010876730301300X International Union of Crystallography en BOOK REVIEW text/html High-resolution electron microscopy. 3rd edition. By John C. H. Spence. Pp. xvi + 401. Oxford University Press, 2003. Price GBP 69.95. ISBN 0-19-850915-4. text 5 59 2003-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 book reviews 513 med@iucr.org 514 1600-5724 http://scripts.iucr.org/cgi-bin/paper?ht5003 Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Thomas, J.M. 2003-07-01 doi:10.1107/S0108767303010845 International Union of Crystallography en text/html Linus Pauling selected scientific papers. Edited by Barclay Kamb, Linda Pauling Kamb, Peter Jeffress Pauling, Alexander Kamb and Linus Pauling Jr. Singapore: World Scientific, 2001. Vols. 1 and 2 set: 1612 pp., USD 114, ISBN 981-02-2784-1; Vol. 1: 864 pp., USD 98, ISBN 981-02-2939-9; Vol. 2: 748 pp., USD 67, ISBN 981-02-2940-2. text 4 59 2003-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 book reviews 434 med@iucr.org 436 1600-5724 http://scripts.iucr.org/cgi-bin/paper?ht5040 Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Grimmer, H. 2003-07-01 doi:10.1107/S0108767303010870 International Union of Crystallography en text/html On quaternions and octonions: their geometry, arithmetic and symmetry. By John H. Conway and Derek A. Smith. Natick, MA: A. K. Peters Ltd, 2003. Price USD 29.00. ISBN 1-56881-134-9 text 4 59 2003-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 book reviews 436 med@iucr.org 436 1600-5724 http://scripts.iucr.org/cgi-bin/paper?bk9109 Wooten [Acta Cryst. (2002), A58, 346–351] defines cells in amorphous Si as being bounded by irreducible rings of atoms, which can be viewed as distorted polygons. These irreducible rings are, roughly speaking, shortest rings. However, the definition used is incomplete and leads to some large rings being counted as irreducible when close examination reveals they are not. In particular, the incomplete definition counts four ninefold rings (out of a total of 1041 ninefold rings) as being irreducible. Yet a detailed examination reveals that these four rings bound a set of smaller rings, and are clearly not irreducible in any meaningful sense of the word. An extended definition has been given [Rivier & Wooten (2003). MATCH – Commun. Math. Comput. Chem. 48, 145–153], and described at length, that removes the difficulties. It results in a small increase in entropy, approaching slightly closer to the ideal. The first paragraph of Wooten (2002) incorrectly states that the nearest-neighbor distance in Si is 3.5 Å, rather than the correct value of 2.35 Å. This misprint has no effect on anything else. Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Wooten, F. 2003-05-01 doi:10.1107/S0108767303007037 International Union of Crystallography Erratum to Acta Cryst. (2002), A58, 346–351. en ENTROPY; AMORPHOUS SILICON; DISORDER Wooten [Acta Cryst. (2002), A58, 346–351] defines cells in amorphous Si as being bounded by irreducible rings of atoms, which can be viewed as distorted polygons. These irreducible rings are, roughly speaking, shortest rings. However, the definition used is incomplete and leads to some large rings being counted as irreducible when close examination reveals they are not. In particular, the incomplete definition counts four ninefold rings (out of a total of 1041 ninefold rings) as being irreducible. Yet a detailed examination reveals that these four rings bound a set of smaller rings, and are clearly not irreducible in any meaningful sense of the word. An extended definition has been given [Rivier & Wooten (2003). MATCH – Commun. Math. Comput. Chem. 48, 145–153], and described at length, that removes the difficulties. It results in a small increase in entropy, approaching slightly closer to the ideal. The first paragraph of Wooten (2002) incorrectly states that the nearest-neighbor distance in Si is 3.5 Å, rather than the correct value of 2.35 Å. This misprint has no effect on anything else. text/html Structure, odd lines and topological entropy of disorder of amorphous silicon. Correction text 3 59 2003-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 addenda and errata 286 med@iucr.org 286 1600-5724 http://scripts.iucr.org/cgi-bin/paper?we0011 A novel and general approach to scaling diffraction intensities is presented. The method minimizes the disagreement among multiple measurements of symmetry-related reflections using a stable refinement procedure. The scale factors are described by a flexible exponential function that allows different scaling corrections to be chosen and combined according to the needs of the experiment. The scaling model presented here includes: scale and temperature factor per batch of data; temperature factor as a continuous function of the radiation dose; absorption in the crystal; uneven exposure within a single diffraction image; and corrections for phenomena that depend on the diffraction peak position on the detector. This scaling model can be extended to include additional corrections for various instrumental and data-collection problems. Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Otwinowski, Z. Borek, D. Majewski, W. Minor, W. 2003-05-01 doi:10.1107/S0108767303005488 International Union of Crystallography A novel method of scaling diffraction intensities is presented. en SCALING; ABSORPTION; DIFFRACTION; EXPONENTIAL MODELLING A novel and general approach to scaling diffraction intensities is presented. The method minimizes the disagreement among multiple measurements of symmetry-related reflections using a stable refinement procedure. The scale factors are described by a flexible exponential function that allows different scaling corrections to be chosen and combined according to the needs of the experiment. The scaling model presented here includes: scale and temperature factor per batch of data; temperature factor as a continuous function of the radiation dose; absorption in the crystal; uneven exposure within a single diffraction image; and corrections for phenomena that depend on the diffraction peak position on the detector. This scaling model can be extended to include additional corrections for various instrumental and data-collection problems. text/html Multiparametric scaling of diffraction intensities text 3 59 2003-05-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 research papers 228 med@iucr.org 234 1600-5724 http://scripts.iucr.org/cgi-bin/paper?ht5027 Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Hart, M. 2003-09-01 doi:10.1107/S0108767303004719 International Union of Crystallography en BOOK RECEIVED text/html The physics of ferroelectric and antiferroelectric liquid crystals. By I. Musevic, R. Blinc & B. Zeks. Singapore: World Scientific, 2000. Pp. 680. USD 129, GBP 88. ISBN 981-02-0325-X text 5 59 2003-09-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 books received 514 med@iucr.org 514 1600-5724 http://scripts.iucr.org/cgi-bin/paper?we9009 In the paper by Feranchuk, Gurskii, Komarov, Lugovskaya, Burgäzy & Ulyanenkov [Acta Cryst. (2002). A58, 370–384], there is a misprint in equation (22): instead of parameter s, the normalized parameter s1 = 4πa0s has to be used, where a0 = 0.529177 Å is a Bohr radius. The conclusions and other results are correct. Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Feranchuk, I.D. Gurskii, L.I. Komarov, L.I. Lugovskaya, O.M. Burgäzy, F. Ulyanenkov, A. 2003-03-01 doi:10.1107/S0108767303002216 International Union of Crystallography Erratum to Acta Cryst. A58, 370–384. en SUSCEPTIBILITY; ATOMIC SCATTERING FACTOR; DEBYE-WALLER FACTOR In the paper by Feranchuk, Gurskii, Komarov, Lugovskaya, Burgäzy & Ulyanenkov [Acta Cryst. (2002). A58, 370–384], there is a misprint in equation (22): instead of parameter s, the normalized parameter s1 = 4πa0s has to be used, where a0 = 0.529177 Å is a Bohr radius. The conclusions and other results are correct. text/html A new method for calculation of crystal susceptibilities for X-ray diffraction at arbitrary wavelength. Erratum text 2 59 2003-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 addenda and errata 199 med@iucr.org 199 1600-5724 http://scripts.iucr.org/cgi-bin/paper?ht5009 Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Steurer, W. 2003-07-01 doi:10.1107/S0108767303001697 International Union of Crystallography en text/html Quasicrystals. The state of the art. (2nd ed.) Edited by D. P. Vincenzo and P. J. Steinhardt. Series on Directions in Condensed Matter Physics, Vol. 16. Pp. xi + 618. Singapore: World Scientific, 1999. Price (hardback) USD 113, GBP 71, ISBN 981-02-4155-0; (paperback) USD 55, GBP 34, ISBN 981-02-4156-9. text 4 59 2003-07-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 book reviews 434 med@iucr.org 434 1600-5724 http://scripts.iucr.org/cgi-bin/paper?ht5000 Copyright (c) 2003 International Union of Crystallography urn:issn:0108-7673 Bryan, R.F. 2003-03-01 doi:10.1107/S0108767302020238 International Union of Crystallography en BOOK REVIEW text/html Fundamentals of crystallography, 2nd edition. Edited by C. Giacovazzo. IUCr Texts on Crystallography 7. Oxford: IUCr/Oxford University Press, 2002. Pp. xxi + 825 + included CD. Price (hardback) GBP 75.00, ISBN 0-19-850957-X; (paperback) GBP 39.50, ISBN 0-19-850958-8. text 2 59 2003-03-01 Acta Crystallographica Section A: Foundations of Crystallography Copyright (c) 2003 International Union of Crystallography 0108-7673 book reviews 200 med@iucr.org 200 1600-5724