Bounding the regularity radius for regular crystals

The new lower bounds for the regularity radius for `regular systems' (orbits of a single point under a crystallographic group) in arbitrary dimension given by Baburin et al. [Acta Cryst. (2018) A74, 616–629] are discussed.

Hyperuniformity and anti-hyperuniformity in one-dimensional substitution tilings

This work examines the long-wavelength scaling properties of self-similar substitution tilings, placing them in their hyperuniformity classes. Quasiperiodic, non-PV (Pisot–Vijayaraghavan number) and limit-periodic examples are analyzed. Novel behavior is demonstrated for certain limit-periodic cases.

Ultrafast calculation of diffuse scattering from atomistic models

A new approach is presented for ultrafast calculation of atomistic diffuse-scattering patterns. It is shown that the fast Fourier transform can be used to perform such calculations rapidly, and a fast method based on sampling theory can be used to reduce high-frequency noise in the calculations.

Ab initio phasing of the diffraction of crystals with translational disorder

This article reports on the combined use of Bragg reflections and diffuse scatter for structure determination in crystallography.

Rotational switches in the two-dimensional fullerene quasicrystal

Local potential differences between the 3⁶ and 3².4.3.4 vertex configurations are identified within a two-dimensional dodecagonal fullerene monolayer. In a local area of the 8/3 approximant, rotational switching fullerenes on 3⁶ vertex sites are revealed by scanning tunneling microscopy.

Aspherical scattering factors for SHELXL – model, implementation and application

A new aspherical scattering factor formalism was implemented in SHELXL. It relies on Gaussian functions and can optionally complement the independent atom model to take into account the deformation of electron-density distribution due to chemical bonding and lone pairs. The automated atom-type assignment was derived from the invariom formalism.

Modeling of energy-dispersive X-ray diffraction for high-symmetry crystal orientation

This article describes the modeling of energy-dispersive X-ray diffraction for high-symmetry crystal orientation. The work gives exact equations for determining the orientation. The results are discussed in terms of basic crystallography, formula applications without limitations, software for exact solutions and equipment.

Determination of stacking ordering in disordered close-packed structures from pairwise correlation functions

It is shown how to reconstruct the stacking sequence from the pairwise correlation functions between layers in close-packed structures using a simulated annealing procedure. The robustness of the procedure is tested with synthetic data, followed by an experimental example.

Reducing dynamical electron scattering reveals hydrogen atoms

Experimental and computational reduction of dynamical electron scattering allows for visualizing of individual hydrogen atoms.

k-Isocoronal tilings

This article presents a method to determine planar edge-to-edge k-isocoronal tilings – tilings whose vertex coronae form k orbits or k transitivity classes under the action of the symmetry group.

Nonlinear optical organic–inorganic crystals: synthesis, structural analysis and verification of harmonic generation in tri-(o-chloro­anilinium nitrate)

This work addresses the structure–property relationship of an interesting organic–inorganic material. The structural investigation is coupled with Hirshfeld surface analysis to examine the nonlinear optical properties.

Selling reduction versus Niggli reduction for crystallographic lattices

The unit-cell reduction described by Selling and used by Delone (Delaunay) is explained in a simple form.

A coloring-book approach to finding coordination sequences

This article presents a simple method for finding formulas for coordination sequences, based on coloring the underlying graph according to certain rules. It is illustrated by applying it to several uniform tilings and their duals.

Anomalous small viral shells and simplest polyhedra with icosahedral symmetry: the rhombic triacontahedron case

The symmetry of the capsomers forming a viral shell determines the polyhedron underlying the shell structure. If the capsid is self-assembled from dimers, this is the rhombic triacontahedron with 30 equivalent rhombic faces.

Updating direct methods

Direct methods techniques are revisited and new mathematical approaches are described.

Model-independent extraction of the shapes and Fourier transforms from patterns of partially overlapped peaks with extended tails

A new method of extracting the individual shapes of overlapping powder peaks with Lorentzian (or other long-range) tails is presented. This allows computation of microstructure directly in Fourier space, without the infamous `hook' problem at low frequency.

Report of the Executive Committee for 2017

Gjønnes Medal in Electron Crystallography – call for nominations

Nominations for the Ewald Prize