issue contents

ISSN: 2053-2733

January 2011 issue

Highlighted illustration

Cover illustration: Polar mode GM6 (left) and antiferrodistortive mode M3-1q (right) present in the monoclinic structure of SrAl2O4, together with a graph of maximal subgroups showing their isotropy subgroups. The amplitude of mode GM6 is much larger, and ab initio calculations confirm its soft character, while distortion M3-1q is a hard mode frozen as an induced secondary distortion [Perez-Mato et al. (2010). Acta Cryst. A66, 558-590]. The mode figures were drawn using FullProf Studio [Rodriguez-Carvajal (1993). Physica B, 192, 55-69].

research papers

Acta Cryst. (2011). A67, 1-8
doi: 10.1107/S0108767310039140
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Algorithms and geometrical properties are described for the automated building of nucleic acids in experimental electron density.

Acta Cryst. (2011). A67, 9-20
doi: 10.1107/S0108767310041437
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The charge-flipping algorithm in its `band-flipping' variant is used to reconstruct density difference between a superstructure and average structure from superstructure reflections only. This technique can be used for the structure solution of superstructures, some types of twins and intergrowths of polytypes as well as for the solution of modulated structures and superstructures of quasicrystals.

Acta Cryst. (2011). A67, 21-34
doi: 10.1107/S010876731004287X
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The practical use of Friedel-difference intensities for space-group determination, least-squares refinement and structure validation is described.

Acta Cryst. (2011). A67, 35-44
doi: 10.1107/S0108767310042431
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Expressions for coincidence indices and bases for coincidence lattices in the hyperbolic plane are obtained using Clifford algebra.

Acta Cryst. (2011). A67, 45-55
doi: 10.1107/S0108767310042297
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A complete table of (3 + 1)D, (3 + 2)D and (3 + 3)D superspace groups has been enumerated that corrects omissions and duplicate entries in previous tables of superspace groups and Bravais classes. A new online data repository provides detailed information about each superspace group.

Acta Cryst. (2011). A67, 56-62
doi: 10.1107/S0108767310044892
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A new real-space implementation of the molecular-replacement method is described, in which the search model vectors are directly matched with the Patterson self and cross vectors. This method enables the searching for small helix fragments in the target crystal and is able to produce fragment-assembled solutions that are structurally homologous to the target structure.

Acta Cryst. (2011). A67, 63-67
doi: 10.1107/S0108767310047823
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A new type of direct methods are presented that directly explore the Patterson instead of the modulus function. Since they work with the experimental intensities, they are particularly well suited for handling powder diffraction data of organic compounds.

Acta Cryst. (2011). A67, 68-86
doi: 10.1107/S0108767310042832
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Given the topology, the lattice together with the set of distance vectors from each atom to the centre of gravity of its neighbours determine the geometry of a crystal structure. A special construction provides the lattice type.

Acta Cryst. (2011). A67, 87-92
doi: 10.1107/S0108767310047513
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It is shown that lattices of subgroups of reducible space groups contain copies of lattices of subgroups of layer and rod groups as sublattices.

short communications

Acta Cryst. (2011). A67, 93-95
doi: 10.1107/S0108767310044296
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The possible range of angles for a triclinic unit cell are explored in detail.

international union of crystallography

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