Crystallography of homophase twisted bilayers: coincidence, union lattices and space groups

A general scheme is proposed to classify and determine the crystallographic properties of twisted bilayers of any homophase 2D structures using complex numbers.

New benchmarks in the modelling of X-ray atomic form factors

Improved analytical representations of X-ray atomic form factors are put forward based on the inverse Mott–Bethe formula. Applying these representations, the mean absolute errors calculated for the complete set of form factors given in Table 6.1.1.1 in International Tables for Crystallography, Vol. C, 3rd ed., are reduced by a factor of ∼50 from previous published analyses. Various form factor compilations are examined to record the applicability of the approach outlined.

Crystal search – feasibility study of a real-time deep learning process for crystallization well images

Four deep learning architectures were applied and SqueezeNet scored best. It was combined with the grid programming system BOINC to realize automatic real-time scoring of crystallization well images. Scores are written to a database and displayed to facilitate image inspection for users.

On automatic determination of quasicrystal orientations by indexing of detected reflections

Indexing of diffraction patterns for application to automatic orientation mapping of quasicrystalline materials is described.

Efficient structure-factor modeling for crystals with multiple components

A multi-component description of the unit-cell content is introduced. Efficient algorithms to define the contribution of these components to structure factors are described and implemented in CCTBX and Phenix.

Double-slit X-ray dynamical diffraction in curved crystals

The double-slit dynamical diffraction of X-rays in curved crystals is theoretically investigated. It is shown that interference fringes similar to Young's fringes are formed which can be used for determination of the curvature radius.

Machine learning for classifying narrow-beam electron diffraction data

Neural networks were trained for robust classification of narrow electron beam diffraction patterns and may significantly decrease the need for storage space.

An invertible seven-dimensional Dirichlet cell characterization of lattices

Starting from a Niggli-reduced cell, a crystallographic lattice may be characterized by seven parameters describing the Dirichlet cell: the three shortest non-coplanar lattice vector lengths, the three shorter of each pair of face-diagonal lengths and the shortest body-diagonal length, from which the Niggli-reduced cell may be recovered.

A note on the wedge reversion antisymmetry operation and 51 types of physical qu­antities in arbitrary dimensions

It is shown that there are 51 types of physical quantities in arbitrary dimensions with distinct transformations by wedge reversion symmetry. In the paper by Gopalan [(2020). Acta Cryst. A76, 318–327] only 41 types were enumerated.

André Authier (1932–2023)

Obituary for André Authier.

Uri Shmueli (1928–2023)

Obituary for Uri Shmueli.