Acta Crystallographica Section A
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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) 2019 International Union of Crystallography2019-11-01International 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 75, Part 6, 2019textweekly62002-01-01T00:00+00:006752019-11-01Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section A: Foundations and Advances778urn:issn:2053-2733med@iucr.orgNovember 20192019-11-01Acta Crystallographica Section Ahttp://journals.iucr.org/logos/rss10a.gif
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Still imageX-ray constrained spin-coupled technique: theoretical details and further assessment of the method
http://scripts.iucr.org/cgi-bin/paper?ae5070
One of the well-established methods of modern quantum crystallography is undoubtedly the X-ray constrained wavefunction (XCW) approach, a technique that enables the determination of wavefunctions which not only minimize the energy of the system under examination, but also reproduce experimental X-ray diffraction data within the limit of the experimental errors. Initially proposed in the framework of the Hartree–Fock method, the strategy has been gradually extended to other techniques of quantum chemistry, but always remaining limited to a single-determinant ansatz for the wavefunction to extract. This limitation has been recently overcome through the development of the novel X-ray constrained spin-coupled (XCSC) approach [Genoni et al. (2018). Chem. Eur. J. 24, 15507–15511] which merges the XCW philosophy with the traditional spin-coupled strategy of valence bond theory. The main advantage of this new technique is the possibility of extracting traditional chemical descriptors (e.g. resonance structure weights) compatible with the experimental diffraction measurements, without the need to introduce information a priori or perform analyses a posteriori. This paper provides a detailed theoretical derivation of the fundamental equations at the basis of the XCSC method and also introduces a further advancement of its original version, mainly consisting in the use of molecular orbitals resulting from XCW calculations at the Hartree–Fock level to describe the inactive electrons in the XCSC computations. Furthermore, extensive test calculations, which have been performed by exploiting high-resolution X-ray diffraction data for salicylic acid and by adopting different basis sets, are presented and discussed. The computational tests have shown that the new technique does not suffer from particular convergence problems. Moreover, all the XCSC calculations provided resonance structure weights, spin-coupled orbitals and global electron densities slightly different from those resulting from the corresponding unconstrained computations. These discrepancies can be ascribed to the capability of the novel strategy to capture the information intrinsically contained in the experimental data used as external constraints.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Genoni, A.Macetti, G.Franchini, D.Pieraccini, S.Sironi, M.2019-09-24doi:10.1107/S2053273319011021International Union of CrystallographyA new method that extends the Jayatilaka X-ray constrained wavefunction approach in the framework of the spin-coupled technique of the valence bond theory is presented. The proposed strategy enables the extraction of traditional chemical information (e.g. weights of resonance structures) from experimental X-ray diffraction data without imposing constraints a priori or performing further analyses a posteriori.ENX-ray constrained wavefunctionquantum crystallographyvalence bond theoryspin-coupled methodOne of the well-established methods of modern quantum crystallography is undoubtedly the X-ray constrained wavefunction (XCW) approach, a technique that enables the determination of wavefunctions which not only minimize the energy of the system under examination, but also reproduce experimental X-ray diffraction data within the limit of the experimental errors. Initially proposed in the framework of the Hartree–Fock method, the strategy has been gradually extended to other techniques of quantum chemistry, but always remaining limited to a single-determinant ansatz for the wavefunction to extract. This limitation has been recently overcome through the development of the novel X-ray constrained spin-coupled (XCSC) approach [Genoni et al. (2018). Chem. Eur. J. 24, 15507–15511] which merges the XCW philosophy with the traditional spin-coupled strategy of valence bond theory. The main advantage of this new technique is the possibility of extracting traditional chemical descriptors (e.g. resonance structure weights) compatible with the experimental diffraction measurements, without the need to introduce information a priori or perform analyses a posteriori. This paper provides a detailed theoretical derivation of the fundamental equations at the basis of the XCSC method and also introduces a further advancement of its original version, mainly consisting in the use of molecular orbitals resulting from XCW calculations at the Hartree–Fock level to describe the inactive electrons in the XCSC computations. Furthermore, extensive test calculations, which have been performed by exploiting high-resolution X-ray diffraction data for salicylic acid and by adopting different basis sets, are presented and discussed. The computational tests have shown that the new technique does not suffer from particular convergence problems. Moreover, all the XCSC calculations provided resonance structure weights, spin-coupled orbitals and global electron densities slightly different from those resulting from the corresponding unconstrained computations. These discrepancies can be ascribed to the capability of the novel strategy to capture the information intrinsically contained in the experimental data used as external constraints.text/htmlX-ray constrained spin-coupled technique: theoretical details and further assessment of the methodtext6752019-09-24Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers778797Crystallography of three-dimensional fluid flows with chirality in hexagonal cases
http://scripts.iucr.org/cgi-bin/paper?eo5102
Magnetic groups are applied to three-dimensional fluid flows with chirality, which are called Beltrami flows (or force-free fields in plasma physics). First, six Beltrami flows are derived so that their symmetries and antisymmetries are described by six different hexagonal magnetic groups. The general Wyckoff positions are used to derive the flows. Special Wyckoff positions are shown to be useful for finding the zero points of the flows. Tube-like surfaces called invariant tori are observed to interlace and form various crystal-like structures when streamlines winding around the surfaces are numerically plotted. Next, two simpler hexagonal Beltrami flows are derived, and their zero points and invariant tori are studied. Some families of the invariant tori have arrangements similar to those observed in materials science.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Nishiyama, T.2019-10-07doi:10.1107/S205327331901146XInternational Union of CrystallographyMagnetic groups are applied to three-dimensional fluid flows with chirality, which are called Beltrami flows. Eight Beltrami flows are derived and studied using Wyckoff positions. The crystal-like structures of their tube-like surfaces, called invariant tori, are numerically observed.ENmagnetic groupschiralityhexagonal symmetryBeltrami flowinvariant torusMagnetic groups are applied to three-dimensional fluid flows with chirality, which are called Beltrami flows (or force-free fields in plasma physics). First, six Beltrami flows are derived so that their symmetries and antisymmetries are described by six different hexagonal magnetic groups. The general Wyckoff positions are used to derive the flows. Special Wyckoff positions are shown to be useful for finding the zero points of the flows. Tube-like surfaces called invariant tori are observed to interlace and form various crystal-like structures when streamlines winding around the surfaces are numerically plotted. Next, two simpler hexagonal Beltrami flows are derived, and their zero points and invariant tori are studied. Some families of the invariant tori have arrangements similar to those observed in materials science.text/htmlCrystallography of three-dimensional fluid flows with chirality in hexagonal casestext6752019-10-07Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers798813Perfect colorings of patterns with multiple orbits
http://scripts.iucr.org/cgi-bin/paper?eo5100
This paper studies colorings of patterns with multiple orbits, particularly those colorings where the orbits share colors. The main problem is determining when such colorings become perfect. This problem is attacked by characterizing all perfect colorings of patterns through the construction of sufficient and necessary conditions for a coloring to be perfect. These results are then applied on symmetrical objects to construct both perfect and non-perfect colorings.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Junio, A.Walo, M.L.2019-10-07doi:10.1107/S2053273319011562International Union of CrystallographyPerfect colorings of patterns with multiple orbits were characterized, with a focus on colorings where the orbits share colors. These results were then applied to construct perfect and non-perfect colorings of various symmetrical objects.ENperfect coloringsmultiple orbitscolor sharingThis paper studies colorings of patterns with multiple orbits, particularly those colorings where the orbits share colors. The main problem is determining when such colorings become perfect. This problem is attacked by characterizing all perfect colorings of patterns through the construction of sufficient and necessary conditions for a coloring to be perfect. These results are then applied on symmetrical objects to construct both perfect and non-perfect colorings.text/htmlPerfect colorings of patterns with multiple orbitstext6752019-10-07Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers814826A universal algorithm for finding the shortest distance between systems of points
http://scripts.iucr.org/cgi-bin/paper?ib5080
Three universal algorithms for geometrical comparison of abstract sets of n points in the Euclidean space R3 are proposed. It is proved that at an accuracy ∊ the efficiency of all the algorithms does not exceed O(n3/∊3/2). The most effective algorithm combines the known Hungarian and Kabsch algorithms, but is free of their deficiencies and fast enough to match hundreds of points. The algorithm is applied to compare both finite (ligands) and periodic (nets) chemical objects.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Blatov, I.A.Kitaeva, E.V.Shevchenko, A.P.Blatov, V.A.2019-10-07doi:10.1107/S2053273319011628International Union of CrystallographyA universal and effective algorithm is proposed for geometrical comparison of abstract sets of n points in Euclidean space. Applications of the algorithm for comparison of both finite (ligands) and periodic (nets) chemical objects are considered.ENsystems of pointsshortest distancealgorithmsThree universal algorithms for geometrical comparison of abstract sets of n points in the Euclidean space R3 are proposed. It is proved that at an accuracy ∊ the efficiency of all the algorithms does not exceed O(n3/∊3/2). The most effective algorithm combines the known Hungarian and Kabsch algorithms, but is free of their deficiencies and fast enough to match hundreds of points. The algorithm is applied to compare both finite (ligands) and periodic (nets) chemical objects.text/htmlA universal algorithm for finding the shortest distance between systems of pointstext6752019-10-07Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers827832Measurement and alleviation of subsurface damage in a thick-crystal neutron interferometer
http://scripts.iucr.org/cgi-bin/paper?vk5038
The construction is described of a monolithic thick-crystal perfect silicon neutron interferometer using an ultra-high-precision grinding technique and a combination of annealing and chemical etching that differs from the construction of prior neutron interferometers. The interferometer is the second to have been annealed after machining and the first to be annealed prior to chemical etching. Monitoring the interference signal at each post-fabrication step provides a measurement of subsurface damage and its alleviation. In this case, the strain caused by subsurface damage manifests itself as a spatially varying angular misalignment between the two relevant volumes of the crystal and is reduced from ∼10−5 rad to ∼10−9 rad by way of annealing and chemical etching.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Heacock, B.Haun, R.Hirota, K.Hosobata, T.Huber, M.G.Jamer, M.E.Kitaguchi, M.Pushin, D.A.Shimizu, H.Taminiau, I.Yamagata, Y.Yamamoto, T.Young, A.R.2019-10-07doi:10.1107/S2053273319011604International Union of CrystallographyThe alleviation of subsurface machining damage in a thick-crystal neutron interferometer is investigated by testing the interferometer throughout an annealing and chemical etching post-fabrication process. Spatially varying Bragg-plane angular misalignments between diffracting components of the interferometer are lessened from 10−5 rad to less than 10−9 rad.ENsiliconinterferometersneutronsmachiningannealingThe construction is described of a monolithic thick-crystal perfect silicon neutron interferometer using an ultra-high-precision grinding technique and a combination of annealing and chemical etching that differs from the construction of prior neutron interferometers. The interferometer is the second to have been annealed after machining and the first to be annealed prior to chemical etching. Monitoring the interference signal at each post-fabrication step provides a measurement of subsurface damage and its alleviation. In this case, the strain caused by subsurface damage manifests itself as a spatially varying angular misalignment between the two relevant volumes of the crystal and is reduced from ∼10−5 rad to ∼10−9 rad by way of annealing and chemical etching.text/htmlMeasurement and alleviation of subsurface damage in a thick-crystal neutron interferometertext6752019-10-07Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers833841X-ray interference fringes from a weakly bent plane-parallel crystal with negative strain gradient
http://scripts.iucr.org/cgi-bin/paper?lk5040
Under the anomalous transmission condition in the Bragg mode, X-ray interference fringes were observed between two beams with different hyperbolic trajectories in a very weakly bent plane-parallel perfect crystal with negative strain gradient. The origin of the fringes was analysed based on the dynamical theory of diffraction for a distorted crystal. In the reflected beam from the entrance surface, the interference fringes were observed between once- and twice-reflected beams from the back surface. In the transmitted beam from the back surface, the interference fringes were observed between the direct beam and once-reflected beam from the entrance surface. In the emitted beam from the lateral surface, the interference fringes were observed between the beams after different numbers of reflections in the crystal. The multiply reflected beams were formed by a combined result of long propagation length along the beam direction with large divergence of the refracted beams when the strain gradient was negative. The period of these interference fringes was sensitive to very weak strain, of the order of 10−7.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Fukamachi, T.Jongsukswat, S.Ju, D.Negishi, R.Hirano, K.Kawamura, T.2019-10-07doi:10.1107/S2053273319011859International Union of CrystallographyIn the waves emitted from the entrance, back and lateral surfaces of a very weakly bent plane-parallel perfect crystal with negative strain gradient, X-ray interference fringes between two refracted beams with different hyperbolic trajectories were observed when the strain was very weak, of the order of 10−7.ENinterference fringesmirage fringesX-ray beam trajectorybent crystalmultiple Bragg diffractiondynamical theory of X-ray diffractionUnder the anomalous transmission condition in the Bragg mode, X-ray interference fringes were observed between two beams with different hyperbolic trajectories in a very weakly bent plane-parallel perfect crystal with negative strain gradient. The origin of the fringes was analysed based on the dynamical theory of diffraction for a distorted crystal. In the reflected beam from the entrance surface, the interference fringes were observed between once- and twice-reflected beams from the back surface. In the transmitted beam from the back surface, the interference fringes were observed between the direct beam and once-reflected beam from the entrance surface. In the emitted beam from the lateral surface, the interference fringes were observed between the beams after different numbers of reflections in the crystal. The multiply reflected beams were formed by a combined result of long propagation length along the beam direction with large divergence of the refracted beams when the strain gradient was negative. The period of these interference fringes was sensitive to very weak strain, of the order of 10−7.text/htmlX-ray interference fringes from a weakly bent plane-parallel crystal with negative strain gradienttext6752019-10-07Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers842850Bayesian machine learning improves single-wavelength anomalous diffraction phasing
http://scripts.iucr.org/cgi-bin/paper?ae5069
Single-wavelength X-ray anomalous diffraction (SAD) is a frequently employed technique to solve the phase problem in X-ray crystallography. The precision and accuracy of recovered anomalous differences are crucial for determining the correct phases. Continuous rotation (CR) and inverse-beam geometry (IBG) anomalous data collection methods have been performed on tetragonal lysozyme and monoclinic survivin crystals and analysis carried out of how correlated the pairs of Friedel's reflections are after scaling. A multivariate Bayesian model for estimating anomalous differences was tested, which takes into account the correlation between pairs of intensity observations and incorporates the a priori knowledge about the positivity of intensity. The CR and IBG data collection methods resulted in positive correlation between I(+) and I(−) observations, indicating that the anomalous difference dominates between these observations, rather than different levels of radiation damage. An alternative pairing method based on near simultaneously observed Bijvoet's pairs displayed lower correlation and it was unsuccessful for recovering useful anomalous differences when using the multivariate Bayesian model. In contrast, multivariate Bayesian treatment of Friedel's pairs improved the initial phasing of the two tested crystal systems and the two data collection methods.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Garcia-Bonete, M.-J.Katona, G.2019-10-07doi:10.1107/S2053273319011446International Union of CrystallographyThe a posteriori probability densities of anomalous structure-factor amplitude differences were estimated by the Markov chain Monte Carlo machine-learning method. The model incorporated the correlation between the different Bijvoet pairs and the improved estimates were shown to be beneficial for SAD phasing.ENsingle-wavelength X-ray anomalous diffractionSADFriedel pairsBijvoet pairscontinuous rotation data collectioninverse-beam geometryBayesian inferencesurvivinSingle-wavelength X-ray anomalous diffraction (SAD) is a frequently employed technique to solve the phase problem in X-ray crystallography. The precision and accuracy of recovered anomalous differences are crucial for determining the correct phases. Continuous rotation (CR) and inverse-beam geometry (IBG) anomalous data collection methods have been performed on tetragonal lysozyme and monoclinic survivin crystals and analysis carried out of how correlated the pairs of Friedel's reflections are after scaling. A multivariate Bayesian model for estimating anomalous differences was tested, which takes into account the correlation between pairs of intensity observations and incorporates the a priori knowledge about the positivity of intensity. The CR and IBG data collection methods resulted in positive correlation between I(+) and I(−) observations, indicating that the anomalous difference dominates between these observations, rather than different levels of radiation damage. An alternative pairing method based on near simultaneously observed Bijvoet's pairs displayed lower correlation and it was unsuccessful for recovering useful anomalous differences when using the multivariate Bayesian model. In contrast, multivariate Bayesian treatment of Friedel's pairs improved the initial phasing of the two tested crystal systems and the two data collection methods.text/htmlBayesian machine learning improves single-wavelength anomalous diffraction phasingtext6752019-10-07Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers851860Relativistic correction of atomic scattering factors for high-energy electron diffraction
http://scripts.iucr.org/cgi-bin/paper?lk5052
Relativistic electron diffraction depends on linear and quadratic terms in the electric potential, the latter being neglected in the frequently used relativistically corrected Schrödinger equation. The quadratic electric potential term modifies atomic scattering amplitudes in particular for large-angle scattering and backscattering. The respective correction increases with increasing scattering angle, increasing atomic number and increasing kinetic energy. Conventional tabulations for electron scattering and its large-angle extrapolations can be amended in closed form by a universal correction based on the screened Coulomb potential squared.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Lentzen, M.2019-10-24doi:10.1107/S2053273319012191International Union of CrystallographyRelativistic electron diffraction depends on linear and quadratic terms in the electric potential, the latter being neglected in the frequently used relativistically corrected Schrödinger equation. Conventional tabulations for electron scattering and its large-angle extrapolations can be amended in closed form by a universal correction based on the screened Coulomb potential squared.ENelectron diffractionatomic scattering factorsrelativity theorySchrödinger equationRelativistic electron diffraction depends on linear and quadratic terms in the electric potential, the latter being neglected in the frequently used relativistically corrected Schrödinger equation. The quadratic electric potential term modifies atomic scattering amplitudes in particular for large-angle scattering and backscattering. The respective correction increases with increasing scattering angle, increasing atomic number and increasing kinetic energy. Conventional tabulations for electron scattering and its large-angle extrapolations can be amended in closed form by a universal correction based on the screened Coulomb potential squared.text/htmlRelativistic correction of atomic scattering factors for high-energy electron diffractiontext6752019-10-24Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers861865A parameter-free double-shear theory for lath martensite
http://scripts.iucr.org/cgi-bin/paper?td5059
A double-shear theory is introduced that predicts the commonly observed {5 5 7}γ habit planes in low-carbon steels. The novelty of this theory is that the shearing systems are chosen in analogy to the original (single-shear) phenomenological theory of martensite crystallography as those that are macroscopically equivalent to twinning. Out of all the resulting double-shear theories, the ones leading to certain {h h k}γ habit planes naturally arise as those having small shape strain magnitude and satisfying a condition of maximal compatibility, thus making any parameter fitting unnecessary. An interesting finding is that the precise coordinates of the predicted {h h k}γ habit planes depend sensitively on the lattice parameters of the face-centered cubic (f.c.c.) and body-centered cubic (b.c.c.) phases. Nonetheless, for various realistic lattice parameters in low-carbon steels, the predicted habit planes are near {5 5 7}γ. The examples of Fe–0.252C and Fe–0.6C are analyzed in detail along with the resulting orientation relationships which are consistently close to the Kurdjumov–Sachs model. Furthermore, a MATLAB app `Lath Martensite' is provided which allows the application of this model to any other material undergoing an f.c.c. to b.c.c. transformation.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Koumatos, K.Muehlemann, A.2019-10-24doi:10.1107/S205327331901252XInternational Union of CrystallographyIn analogy to the original phenomenological theory of martensite crystallography, a double-shear theory for lath martensite is proposed which chooses the shearing systems as those that are macroscopically equivalent to double twinning. Using only the additional assumptions of overall small shape strain magnitude and a condition of maximal compatibility, this approach naturally gives rise to {5 5 7}γ habit planes and orientation relationships close to the Kurdjumov–Sachs model.ENlath martensitedouble shear557 habit planesorientation relationshipsf.c.c. to b.c.c. transformationslow-carbon steelKurdjumov–SachsNishiyama–WassermannA double-shear theory is introduced that predicts the commonly observed {5 5 7}γ habit planes in low-carbon steels. The novelty of this theory is that the shearing systems are chosen in analogy to the original (single-shear) phenomenological theory of martensite crystallography as those that are macroscopically equivalent to twinning. Out of all the resulting double-shear theories, the ones leading to certain {h h k}γ habit planes naturally arise as those having small shape strain magnitude and satisfying a condition of maximal compatibility, thus making any parameter fitting unnecessary. An interesting finding is that the precise coordinates of the predicted {h h k}γ habit planes depend sensitively on the lattice parameters of the face-centered cubic (f.c.c.) and body-centered cubic (b.c.c.) phases. Nonetheless, for various realistic lattice parameters in low-carbon steels, the predicted habit planes are near {5 5 7}γ. The examples of Fe–0.252C and Fe–0.6C are analyzed in detail along with the resulting orientation relationships which are consistently close to the Kurdjumov–Sachs model. Furthermore, a MATLAB app `Lath Martensite' is provided which allows the application of this model to any other material undergoing an f.c.c. to b.c.c. transformation.text/htmlA parameter-free double-shear theory for lath martensitetext6752019-10-24Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers866875Data-driven approach for synchrotron X-ray Laue microdiffraction scan analysis
http://scripts.iucr.org/cgi-bin/paper?ib5076
A novel data-driven approach is proposed for analyzing synchrotron Laue X-ray microdiffraction scans based on machine learning algorithms. The basic architecture and major components of the method are formulated mathematically. It is demonstrated through typical examples including polycrystalline BaTiO3, multiphase transforming alloys and finely twinned martensite. The computational pipeline is implemented for beamline 12.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory. The conventional analytical pathway for X-ray diffraction scans is based on a slow pattern-by-pattern crystal indexing process. This work provides a new way for analyzing X-ray diffraction 2D patterns, independent of the indexing process, and motivates further studies of X-ray diffraction patterns from the machine learning perspective for the development of suitable feature extraction, clustering and labeling algorithms.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Song, Y.Tamura, N.Zhang, C.Karami, M.Chen, X.2019-10-29doi:10.1107/S2053273319012804International Union of CrystallographyA novel data-driven approach for synchrotron Laue X-ray microdiffraction scans is presented based on machine learning techniques.ENsynchrotron X-ray microdiffractiondata-driven analysisPCA labelerunsupervised learningproperty mapsA novel data-driven approach is proposed for analyzing synchrotron Laue X-ray microdiffraction scans based on machine learning algorithms. The basic architecture and major components of the method are formulated mathematically. It is demonstrated through typical examples including polycrystalline BaTiO3, multiphase transforming alloys and finely twinned martensite. The computational pipeline is implemented for beamline 12.3.2 at the Advanced Light Source, Lawrence Berkeley National Laboratory. The conventional analytical pathway for X-ray diffraction scans is based on a slow pattern-by-pattern crystal indexing process. This work provides a new way for analyzing X-ray diffraction 2D patterns, independent of the indexing process, and motivates further studies of X-ray diffraction patterns from the machine learning perspective for the development of suitable feature extraction, clustering and labeling algorithms.text/htmlData-driven approach for synchrotron X-ray Laue microdiffraction scan analysistext6752019-10-29Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers876888Verification of the de Wolff hypothesis concerning the symmetry of β-MnO2
http://scripts.iucr.org/cgi-bin/paper?sc5132
The symmetry lowering from tetragonal to orthorhombic is demonstrated using high-resolution diffraction and also justified by using the magnetic superspace groups formalism for the rutile-type compound β-MnO2. The (lower) orthorhombic symmetry is observed at temperatures both below and above the Néel temperature. The magnetic ordering of β-MnO2 is of spin density type and not screw-type helical. The results support the de Wolff [Acta Cryst. (1959), 12, 341–345] hypothesis about the orthorhombic symmetry of β-MnO2.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Fabrykiewicz, P.Przenioslo, R.Sosnowska, I.Fauth, F.Oleszak, D.2019-11-04doi:10.1107/S2053273319013408International Union of CrystallographyThe de Wolff hypothesis concerning the orthorhombic symmetry of some rutile-type compounds is quantitatively confirmed for β-MnO2 and MnF2.ENβ-MnO2MnF2magnetic orderingmagnetic space groupssymmetryneutron diffractionX-ray diffractionmodulated magnetic structurespyrolusitesuperspace groupsThe symmetry lowering from tetragonal to orthorhombic is demonstrated using high-resolution diffraction and also justified by using the magnetic superspace groups formalism for the rutile-type compound β-MnO2. The (lower) orthorhombic symmetry is observed at temperatures both below and above the Néel temperature. The magnetic ordering of β-MnO2 is of spin density type and not screw-type helical. The results support the de Wolff [Acta Cryst. (1959), 12, 341–345] hypothesis about the orthorhombic symmetry of β-MnO2.text/htmlVerification of the de Wolff hypothesis concerning the symmetry of β-MnO2text6752019-11-04Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers88990119568431956844195684519568461956843195684419568451956846Elastic propagation of fast electron vortices through amorphous materials
http://scripts.iucr.org/cgi-bin/paper?lk5051
This work studies the elastic scattering behavior of electron vortices when propagating through amorphous samples. A formulation of the multislice approach in cylindrical coordinates is used to theoretically investigate the redistribution of intensity between different angular momentum components due to scattering. To corroborate and elaborate on our theoretical results, extensive numerical simulations are performed on three model systems (Si3N4, Fe0.8B0.2, Pt) for a wide variety of experimental parameters to quantify the purity of the vortices, the net angular momentum transfer, and the variability of the results with respect to the random relative position between the electron beam and the scattering atoms. These results will help scientists to further improve the creation of electron vortices and enhance applications involving them.Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Löffler, S.Sack, S.Schachinger, T.2019-11-04doi:10.1107/S2053273319012889International Union of CrystallographyThis article describes the scattering behavior of electron vortices inside amorphous samples. It focuses on the vortex purity, net angular momentum transfer, and statistical variations due to random beam and atom positions.ENelectron vortex beamsamorphous materialselastic scatteringThis work studies the elastic scattering behavior of electron vortices when propagating through amorphous samples. A formulation of the multislice approach in cylindrical coordinates is used to theoretically investigate the redistribution of intensity between different angular momentum components due to scattering. To corroborate and elaborate on our theoretical results, extensive numerical simulations are performed on three model systems (Si3N4, Fe0.8B0.2, Pt) for a wide variety of experimental parameters to quantify the purity of the vortices, the net angular momentum transfer, and the variability of the results with respect to the random relative position between the electron beam and the scattering atoms. These results will help scientists to further improve the creation of electron vortices and enhance applications involving them.text/htmlElastic propagation of fast electron vortices through amorphous materialstext6752019-11-04Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Aresearch papers902910Prices of IUCr journals
http://scripts.iucr.org/cgi-bin/paper?es5018
Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Ashcroft, A.T.2019-10-29doi:10.1107/S2053273319014438International Union of CrystallographyENprices of journalstext/htmlPrices of IUCr journalstext6752019-10-29Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Ainternational union of crystallography911912Berry Phases in Electronic Structure Theory. Electric Polarization, Orbital Magnetization and Topological Insulators. By David Vanderbilt. Cambridge University Press, 2018. Hardback, pp. x+384. Price GBP 59.99. ISBN 9781107157651.
http://scripts.iucr.org/cgi-bin/paper?xo0131
Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733Chaput,L.2019-09-24doi:10.1107/S2053273319009744International Union of CrystallographyENbook reviewBerry phaseselectronic structuretopological insulatorstext/htmlBerry Phases in Electronic Structure Theory. Electric Polarization, Orbital Magnetization and Topological Insulators. By David Vanderbilt. Cambridge University Press, 2018. Hardback, pp. x+384. Price GBP 59.99. ISBN 9781107157651.text6752019-09-24Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Abook reviews913914Islamic Geometric Patterns: Their Historical Development and Traditional Methods of Construction (with a chapter on the use of computer algorithms to generate Islamic geometric patterns by Craig Kaplan). By Jay Bonner. Springer, 2017. Pp. xxv+525. Price USD 139.00. ISBN 978-1-4939-7921-9 (softcover), 978-1-4419-0216-0 (hardcover).
http://scripts.iucr.org/cgi-bin/paper?xo0124
Copyright (c) 2019 International Union of Crystallographyurn:issn:2053-2733McColm, G.2019-10-29doi:10.1107/S2053273319003619International Union of CrystallographyENbook reviewIslamic geometric patternstext/htmlIslamic Geometric Patterns: Their Historical Development and Traditional Methods of Construction (with a chapter on the use of computer algorithms to generate Islamic geometric patterns by Craig Kaplan). By Jay Bonner. Springer, 2017. Pp. xxv+525. Price USD 139.00. ISBN 978-1-4939-7921-9 (softcover), 978-1-4419-0216-0 (hardcover).text6752019-10-29Copyright (c) 2019 International Union of CrystallographyActa Crystallographica Section Abook reviews915918