issue contents

ISSN: 2053-2733

November 2008 issue

Highlighted illustration

Cover illustration: An octagonal mosaic from the Kasbah de Telouet, High Atlas, Morocco, based on a modified quasilattice. The underlying quasilattice can best be seen in the blue-and-black portions of the pattern where the `standing' lozenges define bars of unit width and the diagonally positioned lozenges define bars with a width equal to [square root]2. Four orientations of the bar scheme, 45° apart, and phason shifts (alternation of bars in the sequence) are present. Picture taken by Emil Makovicky during the 24th European Crystallographic Meeting 2007.

research papers

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A novel full-matrix technique for crystallographic macromolecular refinement is described.

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A Bloch-wave model that predicts electron scattering by a dopant atom is derived using perturbation theory. The results are largely confirmed by multislice simulations but subtle differences have also been observed and are attributed to the approximations made in the Bloch-wave model.

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A simple mathematical algorithm is proposed to generate electron-density maps directly from the X-ray diffraction intensities. The maps can reveal the internal structures of macromolecules.

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The Liga algorithm for ab initio determination of some solid-state nanostructures from length lists generated by the atomic pair distribution function is described. Results are demonstrated for ideal Lennard–Jones clusters and experimental C60 data.

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The reliability, reproducibility and influence of refinement parameters of evolutionary algorithm refinements of Monte Carlo simulations have been investigated in analyses of complex disorder and corresponding diffuse scattering from the compound La0.70(1)(Al0.14(1)I0.86(1)). It was found that the resulting structures are qualitatively and quantitatively in good agreement independent of the strategy used. Recommendations for the best choice of the parameters are given.

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An almost periodic function f is sampled at a finite number of points. A new method is developed for discrete computation of finite Fourier expansions of the function that are almost periodic and uniformly approximate f over its entire infinite domain.

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The fast-Fourier-transform-based algorithm maximizing the direct-methods sum function S has been modified to allow the treatment of density functions with positive and negative peaks. Test calculations have been performed on single-crystal X-ray diffraction data, neutron diffraction data and intensities of superstructure reflections.

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The Weigel–Phan–Veysseyre symbols are explained and their properties are described. These symbols are then assigned to the point groups of several families of space E5.

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The definition, properties and symbols of the iso cubic groups are given. The mono cubic crystal families of space En are defined and listed for n = 3 to n = 7. As an application, four crystal families of space E5 are studied in detail.

short communications

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Given the eigenvalue spectrum of a Karle–Hauptman matrix, the phases are uniquely determined if a carefully chosen subset is fixed.

international union of crystallography

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