issue contents

ISSN: 2053-2733

March 2022 issue

Highlighted illustration

Cover illustration: The two commonly used systems of magnetic space-group symbols are those of Belov–Neronova–Smirnova (BNS) and Opechowski–Guccione (OG). Both present challenges of interpretation to novice and expert users alike, which can inhibit understanding and lead to errors in published magnetic structures. To address these challenges going forward, Campbell et al. [Acta Cryst. (2022). A78, 99–106] introduce a new unified (UNI) magnetic space-group symbol, which combines a modified BNS symbol with essential information from the OG symbol. The cover image illustrates a pattern of magnetic moments surrounding the origin of the magnetic space group Pm′-3′, for which the magnetic point group is m′-3′. Operators shown in yellow are time reversed, whereas those shown in blue are not. Magnetic moments are presented as arrows; moments of opposite colors are related by an improper operation. (Image taken from Marc De Graef's web site with permission.)


research papers

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This article introduces a `unified' (UNI) magnetic space-group symbol.

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For single and double, ordinary and grey layer groups G, all the irreducible (half-)integer (co-)representations D(μ)(G) are derived as well as the allowed (co-)representations of the little groups. Band representations for all types of layer groups are induced from the irreducible representations of the site-symmetry groups and decomposed into the irreducible components. Together with many other important characteristics of the layer groups, these results are derived with the program code POLSym and presented at the new web site


research papers

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Local and global constraints mostly determine the value of independence ratios of 2-periodic nets.

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Embeddings of tangled trivalent graphs, with linear connectors (or `sticks') between vertices, are generated under appropriate point-group symmetries, and described. These structures present interesting targets for molecular synthesis of tangled molecules.

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A simplified relationship between the modified O-lattice and the rotation matrix of any Bravais lattice was established for the generation of a coincidence site lattice wherever it exists.

short communications

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A formula for the calculation of the number of Wyckoff sequences of a given space-group type and length is presented, and applied to make a comparison between the calculated frequencies of occurrence of Wyckoff sequences and those observed in the Pearson's Crystal Data Crystal Structure Database for Inorganic Compounds.

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The conjecture of Grosse-Kunstleve et al., that coordination sequences of periodic structures in n-dimensional Euclidean space are rational, is proved. This has been recently proven by Nakamura et al.; however, the proof presented here is a straightforward application of classic techniques from automata theory.
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