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ISSN: 2053-2733

July 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].

research papers


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The change of X-ray diffraction intensities in the presence of a permanent external electric field is modeled in terms of a stationary perturbation theory. Small atomic displacements within a unit cell are recognized as the major origin of structure-factor variations induced by an external electric field. An optimum strategy for X-ray synchrotron diffraction data collection is proposed and assessed using the example of α-GaPO4, considering the limitations of up-to-date experiments.

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A method is described that reconstructs the projected object from coherent images recorded using a scanning transmission electron microscope.

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The growth process of the ridge–trough faces of a twinned crystal is analyzed.

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The electron density of cubic SrTiO3 has been determined from high-quality γ-ray diffraction data and is compared with results reported earlier.

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Use of an area pixel detector using single-photon counting technology has improved the speed of data acquisition and their reliability in grazing-incidence X-ray diffraction experiments at the Swiss Light Source, Paul Scherrer Institute.

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For some types of sphere packing with typical one- and two-dimensional parameter regions, the sphere-packing density as a function of the free parameters is discussed. Some sphere-packing types with extraordinary density properties are presented.

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For all 382 types of homogeneous sphere packings with tetragonal symmetry, minimal sphere-packing densities and sample coordinates are presented. 1- and 2-periodic subunits of these sphere packings are tabulated in addition.

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Two polynomial-time algorithms are developed to solve the integer minimal principle for centrosymmetric structures. These algorithms rely on fast linear algebra techniques to solve the phase problem entirely in reciprocal space.

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The structural parameters of La0.67Ca0.33MnO3 were refined using one-dimensional HOLZ intensities by the QCBED method. It is feasible to obtain reliable structure information by this method and the global optimization algorithm.

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Three-beam Laue–Laue transmission measurements in the vicinity of the K-absorption edge for a small slightly imperfect germanium crystal have been conducted. These reveal that the apparent size of the crystalline medium responsible for the coherent interference is the most important quantity in the interpretation of the ψ profiles. Some evidence points toward a small increase of the f′ values close to the edge compared to tabulated ones.

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The application of statistical diagnostic methods based on leverage analysis to assess the suitability of the results of a crystal-structure model refinement is presented and discussed.

short communications


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Using a quaternion-based characteristic polynomial, a simple algorithm is developed that rapidly and stably determines root mean square deviations for structural superpositions.
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