issue contents

ISSN: 2053-2733

January 2021 issue

Highlighted illustration

Cover illustration: Specific structural repeat units can be used as quasi-unit cells for decagonal quasicrystals. While the Gummelt decagon has been used almost exclusively in the past, in an increasing number of cases Lück decagons have been found to be more appropriate, as shown by Steurer [Acta Cryst. (2021), A77, 36-41]. The cover image shows the electron-density map of decagonal Al-Co-Ni covered with Lück decagons (blue/yellow). A covering with Gummelt decagons (green/yellow) does not fit the stronger peaks properly.


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Authors and readers are reminded of the history and scope of Acta Crystallographica Section A, and simple steps to help maintain its prominence and impact as the premier journal for foundational work in crystallography are outlined.


research papers

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A new web platform is presented for the pair distribution function (PDF) community to use and share advanced PDF analysis software in the cloud.

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The 2D projection of all atomic positions in the β-Mn unit cells shows that they are situated on three circumferences containing 2D projections of 90 vertices of the {3, 3, 5} polytope on the same plane. The exhaustive description of the non-crystallographic symmetry of the β-Mn crystal has been achieved by using the 8D E8 lattice in which both the 4D {3, 3, 5} polytope and cubic 6D B6 lattice can be inserted.

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A phasing algorithm for protein crystallography using diffraction data from multiple crystal forms is proposed. The algorithm is evaluated by simulation, and practical aspects and potential for ab initio phasing are discussed.

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The diversities and commonalities of the two basic decagonal clusters, the Gummelt and the Lück decagons, and of their coverings are discussed.

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The intensity of small-angle X-ray scattering from GaN nanowires on Si(111) depends on the orientation of the side facets with respect to the incident beam. This reminiscence of truncation rod scattering gives rise to a deviation from Porod's law. A roughness of just 3–4 atomic steps per micrometre-long side facet notably changes the intensity curves.

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Relativistic structure factors are used to teach a non-relativistic wavefunction relativity using the X-ray constrained wavefunction method, whereby resolution and scaling effects are critically assessed.

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It is shown that a polyhedron with the trigonal bipyramidal structure is the unique surface area maximizer among all polyhedra with five vertices inscribed in a sphere.

short communications

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A procedure is reported for obtaining an algebraic approximation of the correlation function of a polyhedron starting from its known chord-length distribution.

book reviews

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