Acta Crystallographica Section A

Foundations of Crystallography

Volume 67, Part 1 (January 2011)

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
short communications
international union of crystallography

research papers

Acta Cryst. (2011). A67, 1-8 [ doi:10.1107/S0108767310039140 ]

Geometric properties of nucleic acids with potential for autobuilding

T. Gruene and G. M. Sheldrick

Synopsis: Algorithms and geometrical properties are described for the automated building of nucleic acids in experimental electron density.

Online 11 November 2010

Acta Cryst. (2011). A67, 9-20 [ doi:10.1107/S0108767310041437 ]

Ab initio reconstruction of difference densities by charge flipping

L. Palatinus, F. Fleischer, P. Pattison, T. Weber and W. Steurer

Synopsis: 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.

Online 11 November 2010

Acta Cryst. (2011). A67, 21-34 [ doi:10.1107/S010876731004287X ]

Practical applications of averages and differences of Friedel opposites

H. D. Flack, M. Sadki, A. L. Thompson and D. J. Watkin

Synopsis: The practical use of Friedel-difference intensities for space-group determination, least-squares refinement and structure validation is described.

Online 7 December 2010

Acta Cryst. (2011). A67, 35-44 [ doi:10.1107/S0108767310042431 ]

Coincidence lattices in the hyperbolic plane

M. A. Rodríguez-Andrade, G. Aragón-González, J. L. Aragón and A. Gómez-Rodríguez

Synopsis: Expressions for coincidence indices and bases for coincidence lattices in the hyperbolic plane are obtained using Clifford algebra.

Online 11 November 2010

Acta Cryst. (2011). A67, 45-55 [ doi:10.1107/S0108767310042297 ]

Generation of (3 + d)-dimensional superspace groups for describing the symmetry of modulated crystalline structures

H. T. Stokes, B. J. Campbell and S. van Smaalen

Synopsis: 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.

Online 18 November 2010

Acta Cryst. (2011). A67, 56-62 [ doi:10.1107/S0108767310044892 ]

PVMR: assembling small helix fragments as structural solutions for molecular replacement

F. Jiang and W. Ding

Synopsis: 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.

Online 7 December 2010

Acta Cryst. (2011). A67, 63-67 [ doi:10.1107/S0108767310047823 ]

Patterson-function direct methods for structure determination of organic compounds from powder diffraction data. XVI

J. Rius

Synopsis: 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.

Online 7 December 2010

Acta Cryst. (2011). A67, 68-86 [ doi:10.1107/S0108767310042832 ]

Euclidian embeddings of periodic nets: definition of a topologically induced complete set of geometric descriptors for crystal structures

J.-G. Eon

Synopsis: 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.

Online 15 December 2010

Acta Cryst. (2011). A67, 87-92 [ doi:10.1107/S0108767310047513 ]

Isomorphism of lattices of subgroups of the layer and rod groups with sublattices of subgroups of the space groups

J. Fuksa and V. Kopský

Synopsis: It is shown that lattices of subgroups of reducible space groups contain copies of lattices of subgroups of layer and rod groups as sublattices.

Online 15 December 2010