A symmetry roadmap to new perovskite multiferroics

The new approach to the design of technologically important perovskites described by Senn and Bristowe [Acta Cryst. (2018), A74, 308–321] is discussed.

Precise implications for real-space pair distribution function modeling of effects intrinsic to modern time-of-flight neutron diffractometers

A systematic overview of the effects of common aberrations in time-of-flight neutron powder diffraction data on real-space pair distribution functions is provided, and methods and best practices to mitigate these effects are discussed.

A group-theoretical approach to enumerating magnetoelectric and multiferroic couplings in perovskites

A symmetry-motivated approach for designing perovskites with ferroic and magnetoelectric couplings is proposed. The results highlight which kinds of magnetic orderings and structural distortions need to coexist within the same structure to produce the desired couplings.

A numerical method for deriving shape functions of nanoparticles for pair distribution function refinements

A numerical method for generating shape functions of non-spherical nanoparticles for use in small-box refinements of pair distribution function data is presented and implemented on several sets of simulated and experimental data. With this approach, physically relevant size parameters for simple and complex nanoparticle shapes can be refined from the data.

Plesiotwins versus diperiodic twins

The reticular conditions for the occurrence of plesiotwins and diperiodic twins are systematically analysed.

X-ray molecular orbital analysis. I. Quantum mechanical and crystallographic framework

Molecular orbitals of an organic compound were successfully obtained by X-ray molecular orbital analysis. The quantum-mechanical and crystallographic framework of the method is described.

A Markov theoretic description of stacking-disordered aperiodic crystals including ice and opaline silica

Aperiodic crystals, including ice and opaline silica, are described using a hidden Markov model, deriving expressions for the scattering cross sections. The reversibility of aperiodic crystals is discussed.

Indexing of grazing-incidence X-ray diffraction patterns: the case of fibre-textured thin films

Crystal structure solutions from fibre-textured crystals within thin films are frequently achieved by grazing-incidence X-ray diffraction experiments. In the present work, analytical mathematical expressions are derived for the indexing of experimental diffraction patterns.

Primitive substitution tilings with rotational symmetries

The idea of symmetry order, which describes the rotational symmetry types of tilings in the hull of a given substitution, is introduced. Two substitutions giving rise to six- and sevenfold rotation-invariant tilings are also presented.

Spatio-temporal symmetry – crystallographic point groups with time translations and time inversion

Spatio-temporal crystallographic point groups with time translations and time inversion are derived and tabulated.

Ted Janssen (1936–2017)

Obituary for Ted Janssen.

Quantum Field Theory and Condensed Matter. An Introduction