Acta Crystallographica Section A
//journals.iucr.org/a/issues/2018/02/00/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) 2018 International Union of Crystallography2018-03-01International 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 74, Part 2, 2018textweekly62002-01-01T00:00+00:002742018-03-01Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section A: Foundations and Advances75urn:issn:2053-2733med@iucr.orgMarch 20182018-03-01Acta Crystallographica Section Ahttp://journals.iucr.org/logos/rss10a.gif
//journals.iucr.org/a/issues/2018/02/00/isscontsbdy.html
Still imageSpatial displacement of forward-diffracted X-ray beams by perfect crystals
http://scripts.iucr.org/cgi-bin/paper?sc5112
Time-delayed, narrow-band echoes generated by forward Bragg diffraction of an X-ray pulse by a perfect thin crystal are exploited for self-seeding at hard X-ray free-electron lasers. Theoretical predictions indicate that the retardation is strictly correlated to a transverse displacement of the echo pulses. This article reports the first experimental observation of the displaced echoes. The displacements are in good agreement with simulations relying on the dynamical diffraction theory. The echo signals are characteristic for a given Bragg reflection, the structure factor and the probed interplane distance. The reported results pave the way to exploiting the signals as an online diagnostic tool for hard X-ray free-electron laser seeding and for dynamical diffraction investigations of strain at the femtosecond timescale.Copyright (c) 2018 A. Rodriguez-Fernandez et al.urn:issn:2053-2733Rodriguez-Fernandez, A.Esposito, V.Sanchez, D.F.Finkelstein, K.D.Juranic, P.Staub, U.Grolimund, D.Reiche, S.Pedrini, B.2018-02-23doi:10.1107/S2053273318001419International Union of CrystallographyThe first experimental observation of transverse spatial echoes generated by forward Bragg diffraction of an X-ray beam propagating through a perfect thin crystal is reported.ENX-ray dynamical diffractionperfect crystalstransverse echo displacementhard X-ray self-seedingTime-delayed, narrow-band echoes generated by forward Bragg diffraction of an X-ray pulse by a perfect thin crystal are exploited for self-seeding at hard X-ray free-electron lasers. Theoretical predictions indicate that the retardation is strictly correlated to a transverse displacement of the echo pulses. This article reports the first experimental observation of the displaced echoes. The displacements are in good agreement with simulations relying on the dynamical diffraction theory. The echo signals are characteristic for a given Bragg reflection, the structure factor and the probed interplane distance. The reported results pave the way to exploiting the signals as an online diagnostic tool for hard X-ray free-electron laser seeding and for dynamical diffraction investigations of strain at the femtosecond timescale.text/htmlSpatial displacement of forward-diffracted X-ray beams by perfect crystalstext2742018-02-23Copyright (c) 2018 A. Rodriguez-Fernandez et al.Acta Crystallographica Section Aresearch papers7587The development of powder profile refinement at the Reactor Centre Netherlands at Petten
http://scripts.iucr.org/cgi-bin/paper?ib5058
With thousands of references to `Rietveld refinement' it is forgotten that the method did not suddenly appear in a flash of inspiration of a single person, but was the result of the work of three individuals working in the 1960s at the Reactor Centre Netherlands at Petten, Loopstra, van Laar and Rietveld. This paper outlines the origins of `profile refinement', as it was called at Petten, and also looks at why it took so long for the scientific community to recognize its importance. With the recent passing of Hugo Rietveld, the death of Bert Loopstra in 1998 and before other pioneers also disappear, it is important to set down a first-hand account.Copyright (c) 2018 Bob van Laar and Henk Schenkurn:issn:2053-2733van Laar, B.Schenk, H.2018-03-01doi:10.1107/S2053273317018435International Union of CrystallographyAround 1965 at the Reactor Centre Netherlands at Petten, Loopstra, van Laar and Rietveld developed `profile refinement'. Although Loopstra had the idea, van Laar worked it out mathematically and Rietveld wrote the computer program, the essential contributions of the first two are forgotten when using `Rietveld refinement'.ENpowder profile refinementprofile refinementRietveld refinementWith thousands of references to `Rietveld refinement' it is forgotten that the method did not suddenly appear in a flash of inspiration of a single person, but was the result of the work of three individuals working in the 1960s at the Reactor Centre Netherlands at Petten, Loopstra, van Laar and Rietveld. This paper outlines the origins of `profile refinement', as it was called at Petten, and also looks at why it took so long for the scientific community to recognize its importance. With the recent passing of Hugo Rietveld, the death of Bert Loopstra in 1998 and before other pioneers also disappear, it is important to set down a first-hand account.text/htmlThe development of powder profile refinement at the Reactor Centre Netherlands at Pettentext2742018-03-01Copyright (c) 2018 Bob van Laar and Henk SchenkActa Crystallographica Section Ascientific comment8892Ab initio structure determination and quantitative disorder analysis on nanoparticles by electron diffraction tomography
http://scripts.iucr.org/cgi-bin/paper?vk5023
Nanoscaled porous materials such as zeolites have attracted substantial attention in industry due to their catalytic activity, and their performance in sorption and separation processes. In order to understand the properties of such materials, current research focuses increasingly on the determination of structural features beyond the averaged crystal structure. Small particle sizes, various types of disorder and intergrown structures render the description of structures at atomic level by standard crystallographic methods difficult. This paper reports the characterization of a strongly disordered zeolite structure, using a combination of electron exit-wave reconstruction, automated diffraction tomography (ADT), crystal disorder modelling and electron diffraction simulations. Zeolite beta was chosen for a proof-of-principle study of the techniques, because it consists of two different intergrown polymorphs that are built from identical layer types but with different stacking sequences. Imaging of the projected inner Coulomb potential of zeolite beta crystals shows the intergrowth of the polymorphs BEA and BEB. The structures of BEA as well as BEB could be extracted from one single ADT data set using direct methods. A ratio for BEA/BEB = 48:52 was determined by comparison of the reconstructed reciprocal space based on ADT data with simulated electron diffraction data for virtual nanocrystals, built with different ratios of BEA/BEB. In this way, it is demonstrated that this smart interplay of the above-mentioned techniques allows the elaboration of the real structures of functional materials in detail – even if they possess a severely disordered structure.Copyright (c) 2018 International Union of Crystallographyurn:issn:2053-2733Krysiak, Y.Barton, B.Marler, B.Neder, R.B.Kolb, U.2018-02-15doi:10.1107/S2053273317018277International Union of CrystallographyA routine to extract diffuse-scattering intensities caused by two-dimensional crystalline defects from tomographic electron diffraction data and an algorithm for comparison with simulated diffraction data were developed and applied to intergrown zeolite beta A and zeolite beta B.ENzeolite betadisorder simulationelectron diffraction tomographyin-line electron holographypolytypismNanoscaled porous materials such as zeolites have attracted substantial attention in industry due to their catalytic activity, and their performance in sorption and separation processes. In order to understand the properties of such materials, current research focuses increasingly on the determination of structural features beyond the averaged crystal structure. Small particle sizes, various types of disorder and intergrown structures render the description of structures at atomic level by standard crystallographic methods difficult. This paper reports the characterization of a strongly disordered zeolite structure, using a combination of electron exit-wave reconstruction, automated diffraction tomography (ADT), crystal disorder modelling and electron diffraction simulations. Zeolite beta was chosen for a proof-of-principle study of the techniques, because it consists of two different intergrown polymorphs that are built from identical layer types but with different stacking sequences. Imaging of the projected inner Coulomb potential of zeolite beta crystals shows the intergrowth of the polymorphs BEA and BEB. The structures of BEA as well as BEB could be extracted from one single ADT data set using direct methods. A ratio for BEA/BEB = 48:52 was determined by comparison of the reconstructed reciprocal space based on ADT data with simulated electron diffraction data for virtual nanocrystals, built with different ratios of BEA/BEB. In this way, it is demonstrated that this smart interplay of the above-mentioned techniques allows the elaboration of the real structures of functional materials in detail – even if they possess a severely disordered structure.text/htmlAb initio structure determination and quantitative disorder analysis on nanoparticles by electron diffraction tomographytext2742018-02-15Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section Aresearch papers93101Electron-density critical points analysis and catastrophe theory to forecast structure instability in periodic solids
http://scripts.iucr.org/cgi-bin/paper?kx5065
The critical points analysis of electron density, i.e. ρ(x), from ab initio calculations is used in combination with the catastrophe theory to show a correlation between ρ(x) topology and the appearance of instability that may lead to transformations of crystal structures, as a function of pressure/temperature. In particular, this study focuses on the evolution of coalescing non-degenerate critical points, i.e. such that ∇ρ(xc) = 0 and λ1, λ2, λ3 ≠ 0 [λ being the eigenvalues of the Hessian of ρ(x) at xc], towards degenerate critical points, i.e. ∇ρ(xc) = 0 and at least one λ equal to zero. The catastrophe theory formalism provides a mathematical tool to model ρ(x) in the neighbourhood of xc and allows one to rationalize the occurrence of instability in terms of electron-density topology and Gibbs energy. The phase/state transitions that TiO2 (rutile structure), MgO (periclase structure) and Al2O3 (corundum structure) undergo because of pressure and/or temperature are here discussed. An agreement of 3–5% is observed between the theoretical model and experimental pressure/temperature of transformation.Copyright (c) 2018 International Union of Crystallographyurn:issn:2053-2733Merli, M.Pavese, A.2018-02-15doi:10.1107/S2053273317018381International Union of CrystallographyElectron-density topology is used to detect instability in periodic solids.ENelectron-density critical pointscatastrophe theoryphase/state transitions in crystalsab initio calculationsThe critical points analysis of electron density, i.e. ρ(x), from ab initio calculations is used in combination with the catastrophe theory to show a correlation between ρ(x) topology and the appearance of instability that may lead to transformations of crystal structures, as a function of pressure/temperature. In particular, this study focuses on the evolution of coalescing non-degenerate critical points, i.e. such that ∇ρ(xc) = 0 and λ1, λ2, λ3 ≠ 0 [λ being the eigenvalues of the Hessian of ρ(x) at xc], towards degenerate critical points, i.e. ∇ρ(xc) = 0 and at least one λ equal to zero. The catastrophe theory formalism provides a mathematical tool to model ρ(x) in the neighbourhood of xc and allows one to rationalize the occurrence of instability in terms of electron-density topology and Gibbs energy. The phase/state transitions that TiO2 (rutile structure), MgO (periclase structure) and Al2O3 (corundum structure) undergo because of pressure and/or temperature are here discussed. An agreement of 3–5% is observed between the theoretical model and experimental pressure/temperature of transformation.text/htmlElectron-density critical points analysis and catastrophe theory to forecast structure instability in periodic solidstext2742018-02-15Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section Aresearch papers102111Coordination numbers of the vertex graph of a Penrose tiling
http://scripts.iucr.org/cgi-bin/paper?eo5079
A new approach to study coordination shells and coordination sequences of quasiperiodic graphs is suggested. The structure of the coordination shells in the vertex graph of a Penrose tiling is described. An asymptotic formula for its coordination numbers is obtained. An essentially different behaviour of the coordination numbers for even and odd shells is revealed.Copyright (c) 2018 International Union of Crystallographyurn:issn:2053-2733Shutov, A.Maleev, A.2018-02-15doi:10.1107/S2053273318000062International Union of CrystallographyA description of the coordination sequence of the vertex graph of a Penrose tiling is obtained.ENvertex graphsPenrose tilingsquasiperiodic graphscoordination sequencesA new approach to study coordination shells and coordination sequences of quasiperiodic graphs is suggested. The structure of the coordination shells in the vertex graph of a Penrose tiling is described. An asymptotic formula for its coordination numbers is obtained. An essentially different behaviour of the coordination numbers for even and odd shells is revealed.text/htmlCoordination numbers of the vertex graph of a Penrose tilingtext2742018-02-15Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section Aresearch papers112122Phasing via pure crystallographic least squares: an unexpected feature
http://scripts.iucr.org/cgi-bin/paper?sc5113
Crystallographic least-squares techniques, the main tool for crystal structure refinement of small and medium-size molecules, are for the first time used for ab initio phasing. It is shown that the chief obstacle to such use, the least-squares severe convergence limits, may be overcome by a multi-solution procedure able to progressively recognize and discard model atoms in false positions and to include in the current model new atoms sufficiently close to correct positions. The applications show that the least-squares procedure is able to solve many small structures without the use of important ancillary tools: e.g. no electron-density map is calculated as a support for the least-squares procedure.Copyright (c) 2018 International Union of Crystallographyurn:issn:2053-2733Burla, M.C.Carrozzini, B.Cascarano, G.L.Giacovazzo, C.Polidori, G.2018-02-23doi:10.1107/S2053273318001407International Union of CrystallographyCrystallographic least-squares techniques, a fundamental tool for crystal structure refinement, are used for the first time for ab initio crystal structure solution. No help was needed from other phasing techniques, such as the calculation of electron-density maps.ENphasingleast squaressmall moleculesCrystallographic least-squares techniques, the main tool for crystal structure refinement of small and medium-size molecules, are for the first time used for ab initio phasing. It is shown that the chief obstacle to such use, the least-squares severe convergence limits, may be overcome by a multi-solution procedure able to progressively recognize and discard model atoms in false positions and to include in the current model new atoms sufficiently close to correct positions. The applications show that the least-squares procedure is able to solve many small structures without the use of important ancillary tools: e.g. no electron-density map is calculated as a support for the least-squares procedure.text/htmlPhasing via pure crystallographic least squares: an unexpected featuretext2742018-02-23Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section Aresearch papers123130Development of a joint refinement model for the spin-resolved one-electron reduced density matrix using different data sets
http://scripts.iucr.org/cgi-bin/paper?kx5064
The paper describes a joint refinement model of the spin-resolved one-electron reduced density matrix using simultaneously magnetic structure factors and magnetic directional Compton profiles. The model is guided by two strategies: (i) variation of basis functions and (ii) variation of the spin population matrix. The implementation for a finite system is based on an expansion of the natural orbitals on basis sets. To show the potential benefits brought by the joint refinement model, the paper also presents the refinement results using magnetic structure factors only. The joint refinement model provides very satisfactory results reproducing the pseudo-data. In particular, magnetic Compton profiles have a strong effect not only on the off-diagonal elements of the spin-resolved one-electron reduced density matrix but also on its diagonal elements.Copyright (c) 2018 International Union of Crystallographyurn:issn:2053-2733Gueddida, S.Yan, Z.Gillet, J.-M.2018-03-01doi:10.1107/S2053273318000384International Union of CrystallographyA joint refinement model of the spin-resolved one-electron reduced density matrix is described and validated. The new model provides very satisfactory results.ENone-electron reduced density matrixpolarized neutron diffractionmagnetic Compton scatteringspin density/momentum spin densityjoint refinement modelThe paper describes a joint refinement model of the spin-resolved one-electron reduced density matrix using simultaneously magnetic structure factors and magnetic directional Compton profiles. The model is guided by two strategies: (i) variation of basis functions and (ii) variation of the spin population matrix. The implementation for a finite system is based on an expansion of the natural orbitals on basis sets. To show the potential benefits brought by the joint refinement model, the paper also presents the refinement results using magnetic structure factors only. The joint refinement model provides very satisfactory results reproducing the pseudo-data. In particular, magnetic Compton profiles have a strong effect not only on the off-diagonal elements of the spin-resolved one-electron reduced density matrix but also on its diagonal elements.text/htmlDevelopment of a joint refinement model for the spin-resolved one-electron reduced density matrix using different data setstext2742018-03-01Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section Aresearch papers131142Monoclinic sphere packings. II. Trivariant lattice complexes with mirror symmetry
http://scripts.iucr.org/cgi-bin/paper?eo5081
All homogeneous sphere packings were derived that refer to the three trivariant monoclinic lattice complexes with mirror symmetry. In total, 29 types of sphere packings have been found. Only for three types is the maximal inherent symmetry of their sphere packings monoclinic whereas the inherent symmetry is orthorhombic for 13 types, tetragonal for eight types, hexagonal for four types and cubic for one type.Copyright (c) 2018 International Union of Crystallographyurn:issn:2053-2733Sowa, H.2018-03-01doi:10.1107/S2053273318000475International Union of CrystallographyAll homogeneous sphere packings were derived that refer to the trivariant monoclinic lattice complexes with mirror symmetry.ENsphere packingsmonoclinic crystal systemtrivariant lattice complexesAll homogeneous sphere packings were derived that refer to the three trivariant monoclinic lattice complexes with mirror symmetry. In total, 29 types of sphere packings have been found. Only for three types is the maximal inherent symmetry of their sphere packings monoclinic whereas the inherent symmetry is orthorhombic for 13 types, tetragonal for eight types, hexagonal for four types and cubic for one type.text/htmlMonoclinic sphere packings. II. Trivariant lattice complexes with mirror symmetrytext2742018-03-01Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section Aresearch papers143147The Physics of Solids. By J. B. Ketterson. Oxford University Press, 2016. Pp. 1056. Price GBP 55.00 (hardback). ISBN 9780198742906.
http://scripts.iucr.org/cgi-bin/paper?xo0075
Copyright (c) 2018 International Union of Crystallographyurn:issn:2053-2733Estevez-Rams, E.2018-02-15doi:10.1107/S2053273318002139International Union of CrystallographyENbook reviewsolid-state physicstext/htmlThe Physics of Solids. By J. B. Ketterson. Oxford University Press, 2016. Pp. 1056. Price GBP 55.00 (hardback). ISBN 9780198742906.text2742018-02-15Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section Abook reviews148150Introduction to Many-Body Physics. By Piers Coleman. Cambridge University Press, 2015. Pp. xviii + 796. Price GBP 49.99/USD 84.99 (hardback). ISBN 9780521864886.
http://scripts.iucr.org/cgi-bin/paper?xo0093
Copyright (c) 2018 International Union of Crystallographyurn:issn:2053-2733Lebègue, S.2018-02-23doi:10.1107/S2053273318000633International Union of CrystallographyENbook reviewmany-body physicstext/htmlIntroduction to Many-Body Physics. By Piers Coleman. Cambridge University Press, 2015. Pp. xviii + 796. Price GBP 49.99/USD 84.99 (hardback). ISBN 9780521864886.text2742018-02-23Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section Abook reviews151152Geometry of Crystals, Polycrystals, and Phase Transformations. By Harshad K. D. H. Bhadeshia. CRC Press, 2018. Hardcover, Pp. xv + 251. Price GBP 37.59. ISBN 9781138070783.
http://scripts.iucr.org/cgi-bin/paper?xo0108
Copyright (c) 2018 International Union of Crystallographyurn:issn:2053-2733Nespolo, M.2018-03-01doi:10.1107/S2053273318000645International Union of CrystallographyENbook reviewgeometry of crystalsphase transformationstext/htmlGeometry of Crystals, Polycrystals, and Phase Transformations. By Harshad K. D. H. Bhadeshia. CRC Press, 2018. Hardcover, Pp. xv + 251. Price GBP 37.59. ISBN 9781138070783.text2742018-03-01Copyright (c) 2018 International Union of CrystallographyActa Crystallographica Section Abook reviews153155