issue contents

ISSN: 2053-2733

July 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

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A modified Laue technique suitable for time-resolved diffraction is described in which profile-independent integration is used, the RATIO method is applied and multi-crystal data are normalized to a common scale. The method is applied in single-pulse pump–probe studies of a binuclear Rh complex, showing Rh—Rh bond shortening of 0.136 (8) Å on excitation.

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The correlation of external modulation with diffraction response as a tool to assess the selective diffraction signal and to recover partial phase information is described.

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Molecular-dynamics simulations are used to compare and relate three different types of positional parameters that are of interest to structural scientists.

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Numerical data sets obtained from a series of molecular-dynamics simulations have been used to assess two new anharmonic Debye–Waller factors.

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A novel method is used to determine the amorphous content in the certification of NIST standard reference material (SRM) 676a (corundum). Extrapolation of diffraction measurements from mixtures with Si powders of varying surface-to-volume ratio show that approximately 1% by weight of SRM 676a is amorphous.

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The variance in any point of the electron-density map is estimated for any space group, whether centric or acentric. Calculations may be performed no matter how poor the structure model.

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The linear transformation of standard uncertainties involves the full variance/covariance matrix. A method based on the vec operator is described for the case of second-rank tensors, e.g. anisotropic displacement parameters. This method is also applicable for the calculation of equivalent isotropic displacement parameters (Uequiv), the comparison of refinements in different space-group settings and the calculation of standard uncertainties of eigenvalues.

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The extinction concept is extended for very thin non-ideal crystals. It is shown that for a large gradient the integrated reflected intensity exhibits a prominent extinction minimum caused by X-ray interbranch scattering.

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Small changes in the `shake-and-bake' procedure of direct-methods phasing can extend the minimal resolution for successful applications from 1.2 toward 1.5 Å. These changes also permit the solution of macromolecular structures that are twice as large as those previously solved by these methods.

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The similarity types of parallelohedra are defined and a complete classification of the primitive parallelohedra in Ed, 2 ≤ d ≤ 5, is given.

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Good agreement between the high-resolution experimental results for (222, 113) three-beam diffraction in Ge and computer simulations based on the dynamical multiple diffraction theory are presented.

short communications

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Seitz notation is provided for the symmetry-operations subtables of International Tables for Crystallography, Volume A, Space-Group Symmetry.

international union of crystallography

Acta Cryst. (2011). A67, 419
doi: 10.1107/S0108767311018526
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