issue contents

ISSN: 2053-2733

September 2005 issue

Highlighted illustration

Cover illustration: An experimentally derived plot of the Fermi hole mobility function (FHMF) for urea. The FHMF can be interpreted as a potential energy surface for electron transfer. This plot was obtained from a Hartree-Fock wavefunction constrained to fit measured X-ray diffraction structure factors, using the Tonto program. See Jayatilaka & Grimwood [Acta Cryst. (2004), A60, 111-119].

topical reviews

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In the resonant region near an absorption edge, a polarization anisotropy of the local X-ray susceptibility results in additional reflections otherwise forbidden by screw-axis and/or glide-plane extinction rules.

research papers

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The algebraic approach to the phase problem for the case of X-ray scattering from an ideal crystal is extended to the case of neutron scattering, overcoming the difficulty related to the non-positivity of the scattering density.

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A method is proposed for determining the isomorphism class of nets from their quotient graph, independently of any embedding.

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The X-ray interbranch resonance concept is extended to crystals with a one-dimensional deformation. The new interbranch effect is predicted for a strongly distorted crystal with thickness of the order of the interbranch extinction length.

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The 3D crystal structure of zeolites in the MWW framework family is determined from electron diffraction intensities by direct phasing using maximum entropy and likelihood. Although the `missing cone' left from incomplete goniometric data sampling leads to a somewhat distorted model, the true zeolite framework geometry may be recovered by imposing conservative bonding restraints.

short communications

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Analytical expressions are derived for the polarization factors of three-wave reflections which are functions of the geometrical relations between the relevant crystallographic planes and the spectral and polarization characteristics of the incident radiation.

book reviews

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