Crystallographic descriptions of regular 2-periodic weavings of threads, loops and nets

Crystallographic descriptions are given of regular, piecewise linear embeddings of 2-periodic weavings and polycatenanes.

pinkIndexer – a universal indexer for pink-beam X-ray and electron diffraction snapshots

pinkIndexer, an algorithm developed for indexing of snapshot diffraction patterns recorded with pink-beam X-rays, monochromatic X-rays and electrons, is described and its use evaluated.

Phase of Pendellösung oscillations in X-ray dynamical diffraction for perfect crystals

The phase shift of the Pendellösung oscillations of transmitted and diffracted waves is analyzed in detail for a symmetrical Laue case.

Quasicrystal-related mosaics with periodic lattices interlaid with aperiodic tiles

A new quasicrystal-related solid state is reported, which contains the opposing features of both translational symmetry of crystals and the aperiodicity associated with quasicrystals.

Mathematical aspects of molecular replacement. V. Isolating feasible regions in motion spaces

This paper mathematically characterizes the tiny feasible regions within the vast six-dimensional rotation–translation space in a full molecular replacement (MR) search. The capability to isolate such regions a priori is potentially important for enhancing robustness and efficiency in computational phasing in macromolecular crystallography (MX).

Towards a solution of the inverse X-ray diffraction tomography challenge: theory and iterative algorithm for recovering the 3D displacement field function of Coulomb-type point defects in a crystal

The theoretical framework for a solution of the inverse X-ray diffraction tomography (XRDT) problem is elaborated and a joint quasi-Newton–Levenberg–Marquardt–simulated annealing algorithm is proposed and applied to recovering the 3D displacement field function. It is shown that mesoscopic scale information on crystalline materials can be obtained by the ab initio XRDT technique using 2D imaging patterns with low counting statistics.

On the use of the Obara–Saika recurrence relations for the calculation of structure factors in quantum crystallography

In modern methods of quantum crystallography, electron densities are usually expressed in the form of two-centre expansions involving Cartesian Gaussian-type functions centred on atomic nuclei. Therefore, for the efficient evaluation of structure factors, it is possible to exploit the Obara–Saika method used in quantum chemistry for the evaluation of molecular integrals.

The atomic structure of the Bergman-type icosahedral quasicrystal based on the Ammann–Kramer–Neri tiling

The article discusses the atomic structure modelling based on the Ammann–Kramer–Neri tiling of the ternary Bergman quasicrystal in the 3D real space.

Borates or phosphates? That is the question

New nomenclature is proposed for borates based on quantum chemistry that is in agreement with their properties and recovers the predictive power of Fukunaga and Yamaoka's phase-transition diagram.

On the real combinations of cubes and octahedra

All the real combinations of cubes and octahedra (77657 in total) are enumerated and characterized by facet symbols and symmetry point groups with the most symmetrical forms (163 in total) being suggested as the most probable ones for natural diamond crystals.

Distinguishing space groups by electron channelling: centrosymmetric full-Heusler or non-centrosymmetric half-Heusler?

Electron channelling was successfully used to determine the space group of a crystal where conventional diffraction failed to distinguish between half-Heusler and full-Heusler.

Accurate computation of the rotation matrices. Errata

Two equations in the article by Navaza [Acta Cryst. (1990), A46, 619–620] are corrected.

Multiple Bragg reflection by a thick mosaic crystal. Corrigendum

An inconsistent approximation in Wuttke [Acta Cryst. (2014), A70, 429–440] is corrected. Section 3.5 on the polar angle random walk is withdrawn.

Thermoelectric transport properties in magnetically ordered crystals. Further corrigenda and addenda

Further corrigenda and addenda for the article by Grimmer [Acta Cryst. (2017), A73, 333–345] are reported.

Twenty-Fourth General Assembly and International Congress of Crystallography, Hyderabad, India, 21–28 August 2017

Report of the Executive Committee for 2018

Michael Woolfson (1927–2019)

Obituary for Michael Woolfson

Quantum Theory of Materials

Application-Driven Quantum and Statistical Physics. A Short Course for Future Scientists and Engineers. Volume 1: Foundations. Volume 2: Equilibrium

An Introduction to Clifford Algebras and Spinors