issue contents

ISSN: 2053-2733

November 2020 issue

Highlighted illustration

Cover illustration: In this issue, Fang et al. [Acta Cryst. (2020), A76, 652-663] present a flexible and standalone forward simulation model to compute diffraction projections for laboratory X-ray diffraction contrast tomography, which is a novel technique for non-destructive 3D characterization of grain structures in bulk materials. With this modelling tool detailed analysis of diffraction spots as a function of grain sizes and lattice-plane families for samples with any crystal structure becomes simple and robust. The image shows the simulated diffraction spots (top left), the experimental ones (bottom left) and the comparisons between them (right) for the same grain diffracting at a series of sample rotation angles.


research papers

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The exact potential and multipole moment method for fast and accurate evaluation of the intermolecular electrostatic interaction energies using the pseudoatom-based charge distributions is extended to the calculation of energies in molecular crystal structures. The proposed Ewald and direct summation techniques correctly account for the electron-density penetration effects that in the benchmark systems constitute 24–68% of the total electrostatic interaction energies, and thus cannot be ignored. In agreement with the literature, the Ewald summation method offers a higher precision of the evaluated energies (10−5 kJ mol−1) and a significantly better computational performance.

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A flexible and standalone forward simulation model has been developed to compute the diffraction projections for laboratory diffraction contrast tomography (LabDCT). The outputs are expected to be of great value for all present users of LabDCT as well as interested new users.

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The signal-to-noise ratio and spatial resolution of 3D coherent diffractive imaging are investigated, taking into account the effects of radiation damage to the sample and variability of the incident X-ray intensity. The results are expected to be useful for the design and analysis of X-ray free-electron laser-based imaging experiments.

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The notion of similarity isometries is extended to point packings. A characterization for the similarity isometries of point packings is provided and some planar examples are discusssed. Similarity isometries of point packings about points different from the origin are also examined by studying similarity isometries of shifted point packings.

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High-resolution electron microscopy image contrast obtained from a rutile nanocrystal using direct electron detection is quantified and interpreted based on a model of mosaic crystals.

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It is proved that any parallelo­hedron P as well as tiling by P, except the rhombic dodeca­hedron, can be embedded into the 3D pcu net. It is proved that for the rhombic dodeca­hedron, embedding into the 3D pcu net does not exist; however, embedding into the 4D pcu net does exist. For each parallelo­hedron the deterministic finite automaton is developed which models the growth of the crystalline structure with the same combinatorial type as the given parallelo­hedron.

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Presented here are algorithms for the transformation of lattice basis vectors to a specific target. The algorithms are useful for crystallographic operations in direct and reciprocal spaces alike. The algorithms are demonstrated graphically and numerically.

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A general approach to indexing of diffraction patterns originating from crystals of known structures is presented. Example algorithms are shown to be applicable to patterns of various types, such as Kikuchi patterns, Kossel patterns or Laue patterns.

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Knotted and linked zeolite framework types, based on the sodalite cage (truncated octahedron), are described. Such structures exhibit non-crystallographic symmetry.

international union of crystallography

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