Acta Crystallographica Section A
http://journals.iucr.org/a/issues/2014/05/00/isscontsbdy.html
Acta Crystallographica Section A: Foundations and Advances covers theoretical and fundamental aspects of the structure of matter. The journal is the prime forum for research in diffraction physics and the theory of crystallographic structure determination by diffraction methods using X-rays, neutrons and electrons. The structures include periodic and aperiodic crystals, and non-periodic disordered materials, and the corresponding Bragg, satellite and diffuse scattering, thermal motion and symmetry aspects. Spatial resolutions range from the subatomic domain in charge-density studies to nanodimensional imperfections such as dislocations and twin walls. The chemistry encompasses metals, alloys, and inorganic, organic and biological materials. Structure prediction and properties such as the theory of phase transformations are also covered.enCopyright (c) 2014 International Union of Crystallography2014-08-29International Union of CrystallographyInternational Union of Crystallographyhttp://journals.iucr.orgurn:issn:2053-2733Acta Crystallographica Section A: Foundations and Advances covers theoretical and fundamental aspects of the structure of matter. The journal is the prime forum for research in diffraction physics and the theory of crystallographic structure determination by diffraction methods using X-rays, neutrons and electrons. The structures include periodic and aperiodic crystals, and non-periodic disordered materials, and the corresponding Bragg, satellite and diffuse scattering, thermal motion and symmetry aspects. Spatial resolutions range from the subatomic domain in charge-density studies to nanodimensional imperfections such as dislocations and twin walls. The chemistry encompasses metals, alloys, and inorganic, organic and biological materials. Structure prediction and properties such as the theory of phase transformations are also covered.text/htmlActa Crystallographica Section A: Foundations and Advances, Volume 70, Part 5, 2014textyearly62002-01-01T00:00+00:005702014-08-29Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section A: Foundations and Advances417urn:issn:2053-2733med@iucr.orgAugust 20142014-08-29Acta Crystallographica Section Ahttp://journals.iucr.org/logos/rss10a.gif
http://journals.iucr.org/a/issues/2014/05/00/isscontsbdy.html
Still imageOn the subgroup structure of the hyperoctahedral group in six dimensions
http://scripts.iucr.org/cgi-bin/paper?eo5032
The subgroup structure of the hyperoctahedral group in six dimensions is investigated. In particular, the subgroups isomorphic to the icosahedral group are studied. The orthogonal crystallographic representations of the icosahedral group are classified and their intersections and subgroups analysed, using results from graph theory and their spectra.Copyright (c) 2014 Emilio Zappa et al.urn:issn:2053-2733Zappa, E.Dykeman, E.C.Twarock, R.2014-07-10doi:10.1107/S2053273314007712International Union of CrystallographyThe subgroup structure of the hyperoctahedral group in six dimensions is studied, with particular attention to the subgroups isomorphic to the icosahedral group. The orthogonal crystallographic representations of the icosahedral group are classified, and their intersections are studied in some detail, using a combinatorial approach which involves results from graph theory and their spectra.ENsymmetrycrystallographic representationicosahedral grouphyperoctahedral groupspectral graph theoryThe subgroup structure of the hyperoctahedral group in six dimensions is investigated. In particular, the subgroups isomorphic to the icosahedral group are studied. The orthogonal crystallographic representations of the icosahedral group are classified and their intersections and subgroups analysed, using results from graph theory and their spectra.text/htmlOn the subgroup structure of the hyperoctahedral group in six dimensionstext5702014-07-10Copyright (c) 2014 Emilio Zappa et al.Acta Crystallographica Section Aresearch papers417428Multiple Bragg reflection by a thick mosaic crystal
http://scripts.iucr.org/cgi-bin/paper?sc5071
Symmetric Bragg-case reflections from a thick, ideally imperfect, crystal slab are studied mostly by analytical means. The scattering transfer function of a thin mosaic layer is derived and brought into a form that allows for analytical approximations or easy quadrature. The Darwin–Hamilton equations are generalized, lifting the restriction of wavevectors to a two-dimensional scattering plane. A multireflection expansion shows that wavevector diffusion can be studied independently of the real-space coordinate. Combining analytical arguments and Monte Carlo simulations, multiple Bragg reflections are found to result in a minor correction of the reflected intensity, a moderate broadening of the reflected azimuth angle distribution, a considerable modification of the polar angle distribution, and a noticeable shift and distortion of rocking curves.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Wuttke, J.2014-07-10doi:10.1107/S205327331400802XInternational Union of CrystallographyTo investigate multiple Bragg reflections from a thick and ideally imperfect crystal, the Darwin–Hamilton equations are generalized. Out-of-plane wavevector diffusion causes a noticeable shift and distortion of rocking curves.ENmultiple Bragg reflectionimperfect crystalSymmetric Bragg-case reflections from a thick, ideally imperfect, crystal slab are studied mostly by analytical means. The scattering transfer function of a thin mosaic layer is derived and brought into a form that allows for analytical approximations or easy quadrature. The Darwin–Hamilton equations are generalized, lifting the restriction of wavevectors to a two-dimensional scattering plane. A multireflection expansion shows that wavevector diffusion can be studied independently of the real-space coordinate. Combining analytical arguments and Monte Carlo simulations, multiple Bragg reflections are found to result in a minor correction of the reflected intensity, a moderate broadening of the reflected azimuth angle distribution, a considerable modification of the polar angle distribution, and a noticeable shift and distortion of rocking curves.text/htmlMultiple Bragg reflection by a thick mosaic crystaltext5702014-07-10Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers429440Octagonal symmetry in low-discrepancy β-manganese
http://scripts.iucr.org/cgi-bin/paper?dm5052
A low-discrepancy cubic variant of β-Mn is presented exhibiting local octagonal symmetry upon projection along any of the three mutually perpendicular 〈100〉 axes. Ideal structural parameters are derived to be x(8c) = (2-\sqrt{2})\big/16 and y(12d) = 1\big/(4 \sqrt{2}) for the P4132 enantiomorph. A comparison of the actual and ideal structure models of β-Mn is made in terms of the newly devised concept of geometrical discrepancy maps. Two-dimensional maps of both the geometrical star discrepancy D* and the minimal interatomic distance dmin are calculated over the combined structural parameter range 0 \leq x(8c) \,\lt\, 1/8 and 1/8 \leq y(12d)\, \lt\, 1/4 of generalized β-Mn type structures, showing that the `octagonal' variant of β-Mn is almost optimal in terms of globally minimizing D* while at the same time globally maximizing dmin. Geometrical discrepancy maps combine predictive and discriminatory powers to appear useful within a wide range of structural chemistry studies.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Hornfeck, W.Kuhn, P.2014-07-10doi:10.1107/S2053273314009218International Union of CrystallographyA low-discrepancy cubic variant of β-Mn is presented, exhibiting local octagonal symmetry upon projection. A comparison of the actual and ideal structure models of β-Mn is made in terms of the newly devised concept of geometrical discrepancy maps. Geometrical discrepancy maps combine predictive and discriminatory powers to appear useful within a wide range of structural chemistry studies.ENβ-Mnoctagonal symmetrylow-discrepancycubic variantA low-discrepancy cubic variant of β-Mn is presented exhibiting local octagonal symmetry upon projection along any of the three mutually perpendicular 〈100〉 axes. Ideal structural parameters are derived to be x(8c) = (2-\sqrt{2})\big/16 and y(12d) = 1\big/(4 \sqrt{2}) for the P4132 enantiomorph. A comparison of the actual and ideal structure models of β-Mn is made in terms of the newly devised concept of geometrical discrepancy maps. Two-dimensional maps of both the geometrical star discrepancy D* and the minimal interatomic distance dmin are calculated over the combined structural parameter range 0 \leq x(8c) \,\lt\, 1/8 and 1/8 \leq y(12d)\, \lt\, 1/4 of generalized β-Mn type structures, showing that the `octagonal' variant of β-Mn is almost optimal in terms of globally minimizing D* while at the same time globally maximizing dmin. Geometrical discrepancy maps combine predictive and discriminatory powers to appear useful within a wide range of structural chemistry studies.text/htmlOctagonal symmetry in low-discrepancy β-manganesetext5702014-07-10Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers441447Fast microstructure and phase analyses of nanopowders using combined analysis of transmission electron microscopy scattering patterns
http://scripts.iucr.org/cgi-bin/paper?ib5025
The full quantitative characterization of nanopowders using transmission electron microscopy scattering patterns is shown. This study demonstrates the feasibility of the application of so-called combined analysis, a global approach for phase identification, structure refinement, characterization of anisotropic crystallite sizes and shapes, texture analysis and texture variations with the probed scale, using electron diffraction patterns of TiO2 and Mn3O4 nanocrystal aggregates and platinum films. Electron diffraction pattern misalignments, positioning, and slight changes from pattern to pattern are directly integrated and refined within this approach. The use of a newly developed full-pattern search–match methodology for phase identification of nanopowders and the incorporation of the two-wave dynamical correction for diffraction patterns are also reported and proved to be efficient.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Boullay, P.Lutterotti, L.Chateigner, D.Sicard, L.2014-07-17doi:10.1107/S2053273314009930International Union of CrystallographyThe usefulness of combined analysis for fast determination of crystallite sizes and shapes of nanoparticle aggregates using electron diffraction patterns is demonstrated.ENnanocrystalselectron crystallographyRietveld methodThe full quantitative characterization of nanopowders using transmission electron microscopy scattering patterns is shown. This study demonstrates the feasibility of the application of so-called combined analysis, a global approach for phase identification, structure refinement, characterization of anisotropic crystallite sizes and shapes, texture analysis and texture variations with the probed scale, using electron diffraction patterns of TiO2 and Mn3O4 nanocrystal aggregates and platinum films. Electron diffraction pattern misalignments, positioning, and slight changes from pattern to pattern are directly integrated and refined within this approach. The use of a newly developed full-pattern search–match methodology for phase identification of nanopowders and the incorporation of the two-wave dynamical correction for diffraction patterns are also reported and proved to be efficient.text/htmlFast microstructure and phase analyses of nanopowders using combined analysis of transmission electron microscopy scattering patternstext5702014-07-17Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers448456Strain distributions and diffraction peak profiles from crystals with dislocations
http://scripts.iucr.org/cgi-bin/paper?dm5055
Diffraction profiles for different models of dislocation arrangements are calculated directly by the Monte Carlo method and compared with the strain distributions for the same arrangements, which corresponds to the Stokes–Wilson approximation. It is shown that the strain distributions and the diffraction profiles are in close agreement as long as long-range order is absent. Analytical calculation of the strain distribution for uncorrelated defects is presented. For straight dislocations, the Stokes–Wilson and the Krivoglaz–Wilkens approximations give the same diffraction profiles, with the Gaussian central part and ∝ q−3 power law at the tails.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Kaganer, V.M.Sabelfeld, K.K.2014-07-17doi:10.1107/S2053273314011139International Union of CrystallographyDiffraction profiles for different models of dislocation arrangements are calculated directly by the Monte Carlo method and compared with the strain distributions for the same arrangements, which corresponds to the Stokes–Wilson approximation. The strain distributions and the diffraction profiles are in close agreement as long as long-range order is absent.ENdislocationsMonte Carlo methodspowder diffractionstrainpeak profilesDiffraction profiles for different models of dislocation arrangements are calculated directly by the Monte Carlo method and compared with the strain distributions for the same arrangements, which corresponds to the Stokes–Wilson approximation. It is shown that the strain distributions and the diffraction profiles are in close agreement as long as long-range order is absent. Analytical calculation of the strain distribution for uncorrelated defects is presented. For straight dislocations, the Stokes–Wilson and the Krivoglaz–Wilkens approximations give the same diffraction profiles, with the Gaussian central part and ∝ q−3 power law at the tails.text/htmlStrain distributions and diffraction peak profiles from crystals with dislocationstext5702014-07-17Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers457471Radial spacing distributions from planar point sets
http://scripts.iucr.org/cgi-bin/paper?dm5054
This paper explores the radial projection method for locally finite planar point sets and provides numerical examples for different types of order. The main question is whether the method is suitable to analyse order in a quantitative way. The findings indicate that the answer is affirmative. In this context, local visibility conditions are also studied for certain types of aperiodic point sets.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Baake, M.Götze, F.Huck, C.Jakobi, T.2014-08-30doi:10.1107/S2053273314011140International Union of CrystallographyThe radial projection method for locally finite planar point sets is explored and numerical examples for different types of order are provided.ENaperiodic orderradial spacing distributionsThis paper explores the radial projection method for locally finite planar point sets and provides numerical examples for different types of order. The main question is whether the method is suitable to analyse order in a quantitative way. The findings indicate that the answer is affirmative. In this context, local visibility conditions are also studied for certain types of aperiodic point sets.text/htmlRadial spacing distributions from planar point setstext5702014-08-30Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers472482Hirshfeld atom refinement for modelling strong hydrogen bonds
http://scripts.iucr.org/cgi-bin/paper?kx5029
High-resolution low-temperature synchrotron X-ray diffraction data of the salt l-phenylalaninium hydrogen maleate are used to test the new automated iterative Hirshfeld atom refinement (HAR) procedure for the modelling of strong hydrogen bonds. The HAR models used present the first examples of Z′ > 1 treatments in the framework of wavefunction-based refinement methods. l-Phenylalaninium hydrogen maleate exhibits several hydrogen bonds in its crystal structure, of which the shortest and the most challenging to model is the O—H...O intramolecular hydrogen bond present in the hydrogen maleate anion (O...O distance is about 2.41 Å). In particular, the reconstruction of the electron density in the hydrogen maleate moiety and the determination of hydrogen-atom properties [positions, bond distances and anisotropic displacement parameters (ADPs)] are the focus of the study. For comparison to the HAR results, different spherical (independent atom model, IAM) and aspherical (free multipole model, MM; transferable aspherical atom model, TAAM) X-ray refinement techniques as well as results from a low-temperature neutron-diffraction experiment are employed. Hydrogen-atom ADPs are furthermore compared to those derived from a TLS/rigid-body (SHADE) treatment of the X-ray structures. The reference neutron-diffraction experiment reveals a truly symmetric hydrogen bond in the hydrogen maleate anion. Only with HAR is it possible to freely refine hydrogen-atom positions and ADPs from the X-ray data, which leads to the best electron-density model and the closest agreement with the structural parameters derived from the neutron-diffraction experiment, e.g. the symmetric hydrogen position can be reproduced. The multipole-based refinement techniques (MM and TAAM) yield slightly asymmetric positions, whereas the IAM yields a significantly asymmetric position.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Woińska, M.Jayatilaka, D.Spackman, M.A.Edwards, A.J.Dominiak, P.M.Woźniak, K.Nishibori, E.Sugimoto, K.Grabowsky, S.2014-08-30doi:10.1107/S2053273314012443International Union of CrystallographyDifferent X-ray refinement methods for modelling hydrogen bonds in the compound l-phenylalaninium hydrogen maleate are compared. It is found that Hirshfeld atom refinement (HAR) produces bond lengths involving hydrogen atoms in agreement with benchmarking results from neutron diffraction, and it is the only X-ray method to obtain a symmetric hydrogen site in the intramolecular hydrogen bond of this compound. Residual-density distributions in HAR are better than in the multipole-based models.ENHirshfeld atom refinementelectron densityhydrogen bondsstructure refinementhydrogen maleateaspherical scattering factorsHigh-resolution low-temperature synchrotron X-ray diffraction data of the salt l-phenylalaninium hydrogen maleate are used to test the new automated iterative Hirshfeld atom refinement (HAR) procedure for the modelling of strong hydrogen bonds. The HAR models used present the first examples of Z′ > 1 treatments in the framework of wavefunction-based refinement methods. l-Phenylalaninium hydrogen maleate exhibits several hydrogen bonds in its crystal structure, of which the shortest and the most challenging to model is the O—H...O intramolecular hydrogen bond present in the hydrogen maleate anion (O...O distance is about 2.41 Å). In particular, the reconstruction of the electron density in the hydrogen maleate moiety and the determination of hydrogen-atom properties [positions, bond distances and anisotropic displacement parameters (ADPs)] are the focus of the study. For comparison to the HAR results, different spherical (independent atom model, IAM) and aspherical (free multipole model, MM; transferable aspherical atom model, TAAM) X-ray refinement techniques as well as results from a low-temperature neutron-diffraction experiment are employed. Hydrogen-atom ADPs are furthermore compared to those derived from a TLS/rigid-body (SHADE) treatment of the X-ray structures. The reference neutron-diffraction experiment reveals a truly symmetric hydrogen bond in the hydrogen maleate anion. Only with HAR is it possible to freely refine hydrogen-atom positions and ADPs from the X-ray data, which leads to the best electron-density model and the closest agreement with the structural parameters derived from the neutron-diffraction experiment, e.g. the symmetric hydrogen position can be reproduced. The multipole-based refinement techniques (MM and TAAM) yield slightly asymmetric positions, whereas the IAM yields a significantly asymmetric position.text/htmlHirshfeld atom refinement for modelling strong hydrogen bondstext5702014-08-30Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers4834981005733More about systematic errors in charge-density studies
http://scripts.iucr.org/cgi-bin/paper?eo5030
In order to detect and graphically visualize the absence or presence of systematic errors in fit data, conditional probabilities are employed to analyze the statistical independence or dependence of fit residuals. This concept is completely general and applicable to all scientific fields in which model parameters are fitted to experimental data. The applications presented in this work refer to published charge-density data.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Henn, J.Meindl, K.2014-08-30doi:10.1107/S2053273314012984International Union of CrystallographyMethods for the detection and visualization of systematic errors in measurement data are developed on the basis of conditional probabilities and applied to artificial and experimental data from the literature.ENcharge-density studiesquality indicatorssystematic errorsconditional probabilitystatistical independenceIn order to detect and graphically visualize the absence or presence of systematic errors in fit data, conditional probabilities are employed to analyze the statistical independence or dependence of fit residuals. This concept is completely general and applicable to all scientific fields in which model parameters are fitted to experimental data. The applications presented in this work refer to published charge-density data.text/htmlMore about systematic errors in charge-density studiestext5702014-08-30Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers499513Analysis of multicrystal pump–probe data sets. I. Expressions for the RATIO model
http://scripts.iucr.org/cgi-bin/paper?pc5040
The RATIO method in time-resolved crystallography [Coppens et al. (2009). J. Synchrotron Rad. 16, 226–230] was developed for use with Laue pump–probe diffraction data to avoid complex corrections due to wavelength dependence of the intensities. The application of the RATIO method in processing/analysis prior to structure refinement requires an appropriate ratio model for modeling the light response. The assessment of the accuracy of pump–probe time-resolved structure refinements based on the observed ratios was discussed in a previous paper. In the current paper, a detailed ratio model is discussed, taking into account both geometric and thermal light-induced changes.Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Fournier, B.Coppens, P.2014-08-30doi:10.1107/S2053273314013229International Union of CrystallographyThe application of the RATIO method in processing/analysis prior to structure refinement requires an appropriate ratio model for modeling the light response. Such a model is discussed, taking into account both geometric and thermal light-induced changes.ENRATIO modelmulti-crystal scalingpump–probe experimentdata analysisThe RATIO method in time-resolved crystallography [Coppens et al. (2009). J. Synchrotron Rad. 16, 226–230] was developed for use with Laue pump–probe diffraction data to avoid complex corrections due to wavelength dependence of the intensities. The application of the RATIO method in processing/analysis prior to structure refinement requires an appropriate ratio model for modeling the light response. The assessment of the accuracy of pump–probe time-resolved structure refinements based on the observed ratios was discussed in a previous paper. In the current paper, a detailed ratio model is discussed, taking into account both geometric and thermal light-induced changes.text/htmlAnalysis of multicrystal pump–probe data sets. I. Expressions for the RATIO modeltext5702014-08-30Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Aresearch papers514517Phasing in Crystallography: A Modern Perspective. By Carmelo Giacovazzo. IUCr Texts on Crystallography, No. 20. International Union of Crystallography/Oxford University Press, 2013. Pp. 432. Price GBP 65.00 (hardback). ISBN 978-0-19-968699-5.
http://scripts.iucr.org/cgi-bin/paper?xo0002
Copyright (c) 2014 International Union of Crystallographyurn:issn:2053-2733Blessing, R.H.2014-07-17doi:10.1107/S2053273314010651International Union of CrystallographyENbook reviewtext/htmlPhasing in Crystallography: A Modern Perspective. By Carmelo Giacovazzo. IUCr Texts on Crystallography, No. 20. International Union of Crystallography/Oxford University Press, 2013. Pp. 432. Price GBP 65.00 (hardback). ISBN 978-0-19-968699-5.text5702014-07-17Copyright (c) 2014 International Union of CrystallographyActa Crystallographica Section Abook reviews518519