Acta Crystallographica Section A

Foundations of Crystallography

Volume 54, Part 3 (May 1998)

Cover illustration: Power spectrum of a high-resolution electron-microscopy image of NiAl <110>. The image calculation includes a realistic phonon spectrum by coupling the `molecular dynamics' and `multislice' simulation techniques. The diffuse background, satellite peaks and bands mirror the effect of thermal diffuse scattering and correlated atom vibrations. Courtesy of G. Möbus, T. Gemming and P. Gumbsch.

• research papers
• short communications
• international union of crystallography

research papers

Acta Cryst. (1998). A54, 257-261    [doi:10.1107/S0108767397012798]

On Opechowski-Guccione Magnetic Space-Group Symbols

D. B. Litvin

Synopsis: The meaning of the Opechowski-Guccione magnetic space-group symbols depends on information contained in International Tables for Crystallography. The impact of changes in International Tables for Crystallography on the meaning of these symbols is discussed.

Acta Cryst. (1998). A54, 262-266    [doi:10.1107/S0108767397013597]

On the Use of Eigenvalues and Eigenvectors in the Phase Problem

J. L. van der Plas, R. A. G. de Graaff and H. Schenk

Synopsis: The eigenvalues of large Karle-Hauptman matrices can be predicted using the rank of the matrix and the value of the diagonal elements. The specific properties of the eigenvalues and eigenvectors can be used in solving the phase problem.

Acta Cryst. (1998). A54, 267-272    [doi:10.1107/S0108767397013603]

Karle-Hauptman Matrices and Eigenvalues: a Practical Approach

J. L. van der Plas, R. A. G. de Graaff and H. Schenk

Synopsis: The consequences for the phase problem of the theory developed in an earlier paper, where the properties of the eigenvalue spectrum of a large Karle-Hauptman matrix were derived, are discussed. Practical applications are given.

Acta Cryst. (1998). A54, 273-282    [doi:10.1107/S0108767397016176]

Solving Crystal Structures without Fourier Mapping. I. Centrosymmetric Case

K. Pilz and K. F. Fischer

Synopsis: An algebraic method plus a determinant technique permit the determination of one-dimensional centrosymmetric point-atom structures. In favourable cases, a solution may be proved to be unique.

Acta Cryst. (1998). A54, 283-289    [doi:10.1107/S0108767397016899]

The Influence of Anisotropic Thermal Vibrations on Absorptive Form Factors for High-Energy Electron Diffraction

A. L. Weickenmeier and H. Kohl

Synopsis: A general formula for the absorptive form factors accounting for anisotropic thermal vibrations is given using the Einstein model. A case study shows that even slight deviations from isotropy lead to a strong directional dependence of the absorptive form factors.

Acta Cryst. (1998). A54, 290-295    [doi:10.1107/S0108767397016905]

Symbolic Addition in Protein Electron Crystallography - a Method for Finding Projected Helices

D. L. Dorset

Synopsis: When globular density, e.g. a projected -helix, is treated as a pseudo atom for calculating |E_h|, a protein structure can be determined at low resolution by direct methods. The orthorhombic form of bacteriorhodopsin is treated as an example.

Acta Cryst. (1998). A54, 296-305    [doi:10.1107/S0108767397016917]

A Minimum-Entropy Algorithm for Surface Phasing Problems

L. D. Marks and E. Landree

Synopsis: Development of a minimum-entropy direct-methods approach.

Acta Cryst. (1998). A54, 306-319    [doi:10.1107/S0108767397017030]

Structure Model for the Phase Al_mFe Derived from Three-Dimensional Electron Diffraction Intensity Data Collected by a Precession Technique. Comparison with Convergent-Beam Diffraction

J. Gjønnes, V. Hansen, B. S. Berg, P. Runde, Y. F. Cheng, K. Gjønnes, D. L. Dorset and C. J. Gilmore

Synopsis: The crystal structure of a metastable phase Al_mFe has been determined by application of Patterson analysis and direct methods to a three-dimensional electron diffraction intensity data set of 598 reflections collected by a precession technique.

Acta Cryst. (1998). A54, 320-329    [doi:10.1107/S0108767397017893]

Sphere Packings and Space Filling by Congruent Simple Polyhedra

M. O'Keeffe

Synopsis: 14-coordinated packings of symmetry-related spheres in which all the holes are tetrahedral are described. The dual structures with vertices in the holes of the packings form 4-connected nets that divide space into congruent simple polyhedra.

Acta Cryst. (1998). A54, 330-337    [doi:10.1107/S0108767397018473]

Symmetry and Its Change in Reciprocal Space of a Crystal Simulated by Molecular Dynamics: Application to Quartz

A. Miyake, H. Hasegawa, K. Kawamura and M. Kitamura

Synopsis: The Fourier transformation to calculate structure factors was applied to a crystal simulated by the molecular-dynamics method to clarify the crystallographic symmetry of the crystal and its change during phase transition.

Acta Cryst. (1998). A54, 338-347    [doi:10.1107/S0108767397018849]

Existence of Two Crystal Structures of the Complex -D-Glucose·NaCl·H₂O(2:1:1) Verified by Three-Beam Diffraction Experiments

R. H. Mathiesen, F. Mo, A. Eikenes, T. Nyborg and H. B. Larsen

Synopsis: Triplet phases from three-beam diffraction experiments have been used for structure verification and discrimination between two similar crystal structures of the title complex. This is a novel and potentially powerful application of physically estimated triplet phases.

Acta Cryst. (1998). A54, 348-356    [doi:10.1107/S0108767397019910]

Representation of the Axial Settings of Mica Polytypes

M. Nespolo, H. Takeda and G. Ferraris

Synopsis: Some new definitions, which allow a systematic approach to the indexing of diffraction patterns, are introduced to classify mica polytypes with any number of layers and their axial settings. The transformation rules between settings are given.

short communications

Acta Cryst. (1998). A54, 357    [doi:10.1107/S010876739800124X]

Relativistic X-ray elastic scattering factors for neutral atoms Z = 1-54 from multiconfiguration Dirac-Fock wavefunctions in the 0-12Å^-1 sin,/ range, and six-Gaussian analytical expressions in the 0-6Å^-1 range. Erratum

Z. Su and P. Coppens

Synopsis: Erratum to Acta Cryst. (1997), A 53, 749-762.

international union of crystallography

Acta Cryst. (1998). A54, 358    [doi:10.1107/S0108767398004243]

Nominations for the Ewald Prize

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