Acta Crystallographica Section A

Foundations of Crystallography

Volume 52, Part 5 (September 1996)

Cover illustration: Indicatrix of the inverse of Young's modulus for ADP, a tetragonal crystal. Courtesy of A. Authier, Laboratoire de Minéralogie-Cristallographie, Université Pierre et Marie Curie, Paris, France.

research papers
short communications
letters to the editor
international union of crystallography

research papers

Acta Cryst. (1996). A52, 649-658 [ doi:10.1107/S0108767396003960 ]

Relativistic X-ray Elastic Scattering Factors for He-Ar from Dirac-Hartree-Fock Wave Functions

J. Wang, V. H. Smith Jnr, C. F. Bunge and R. Jáuregui

Synopsis: Relativisitic X-ray and electron scattering factors for first- and second-row atoms and ions are tabulated. The present results are based on multiconfiguration Dirac-Hartree-Fock calculations which have the correct non-relativistic limit and will allow relativistic contributions to the scattering factors to be extracted properly.

Acta Cryst. (1996). A52, 659-668 [ doi:10.1107/S0108767396004370 ]

Improved Structure Refinement Through Maximum Likelihood

N. S. Pannu and R. J. Read

Synopsis: Maximum-likelihood refinement can improve a protein structure more than twice as much as least-squares refinement.

Acta Cryst. (1996). A52, 669-674 [ doi:10.1107/S0108767396004175 ]

Observation of Phase Change of X-ray Polarizability in Rocking Curves

T. Fukamachi, R. Negishi, S. Zhou, M. Yoshizawa, T. Sakamaki, T. Kawamura and T. Nakajima

Synopsis: By measurement of the change of asymmetry of the transmitted rocking curves for GaAs 200 diffraction near K-absorption edges, the phase change of the structure factors was examined.

Acta Cryst. (1996). A52, 675-680 [ doi:10.1107/S010876739600431X ]

The Phase Problem in Structure Analysis and its One-Dimensional Solution

H. Jagodzinski

Synopsis: A new approach to the one-dimensional solution of the phase problem in diffraction is given, introducing periodic Fourier transforms of shift functions.

Acta Cryst. (1996). A52, 681-685 [ doi:10.1107/S0108767396004540 ]

Maximal Subgroups of Magnetic Space Groups and Subperiodic Groups

D. B. Litvin

Synopsis: A method is given for the derivation of the maximal subgroups of magnetic space groups and subperiodic groups.

Acta Cryst. (1996). A52, 686-699 [ doi:10.1107/S0108767396004576 ]

Dynamical Effects of High-Energy Diffraction in Non-centrosymmetric Sphalerite, ZnS

H. Matsuhata and J. Gjønnes

Synopsis: Dynamical effects in high-energy electron diffraction were observed in sphalerite, ZnS. The structure factors of lower angle were measured.

Acta Cryst. (1996). A52, 700-704 [ doi:10.1107/S0108767396004631 ]

Elimination of Extinction Effects by Extrapolation to Zero Wavelength

J. R. Hester and F. P. Okamura

Synopsis: The practicality of extrapolating multiple-wavelength single- crystal intensity measurements to zero wavelength for extinc- tion-correction purposes is investigated.

Acta Cryst. (1996). A52, 705-711 [ doi:10.1107/S0108767396004643 ]

The Electrostatic Contribution to the Forward-Scattering Potential at aSpace Charge Layer in High-Energy Electron Diffraction. I. Theory Neglecting the Effects of Fringing Fields

R. E. Dunin-Borkowski, W. O. Saxton and W. M. Stobbs

Synopsis: Expressions for the electrostatic potential at an interfacial space charge layer are determined using classical electrostatics, with particular reference to the use of phase-contrast techniques in transmission electron microscopy for characterizing such layers. Both the sensitivity of the potential to the detailed form of the charge distribution and the effect of the internal electric field on the strain within the material are discussed.

Acta Cryst. (1996). A52, 712-716 [ doi:10.1107/S0108767396004886 ]

Derivation of the Joint Probability Distribution of Structure-Factor Components Without Assuming Independent Atoms: Relation to the Sparse-Density Principle

P. Verwer, H. Krabbendam and J. Kroon

Synopsis: A number of equations based on the sparse-density principle are derived, along with the corresponding j.p.d.'s, and the effect of the assumption of independent atoms is investigated.

Acta Cryst. (1996). A52, 717-729 [ doi:10.1107/S0108767396005338 ]

Electron Statistical Dynamical Diffuse Scattering in Crystals Containing Short-Range-Order Point Defects

Z. L. Wang

Synopsis: A formal statistical dynamical theory is developed to calculate Bragg and diffuse scattering produced by short-range order (SRO) in a distorted crystal structure with consideration of atomic thermal vibrations. A rigorous proof is given to show the inclusion of a complex potential in the dynamical calculation automatically recovers the contributions made by the high-order diffuse scattering, although the calculation is done using the equation derived under the distorted-wave Born approximation.

Acta Cryst. (1996). A52, 730-747 [ doi:10.1107/S0108767396005727 ]

Diffraction-Line Broadening due to Strain Fields in Materials; Fundamental Aspects and Methods of Analysis

J. G. M. van Berkum, R. Delhez, Th. H. de Keijser and E. J. Mittemeijer

Synopsis: Diffraction-line broadening due to strain fields in materials is discussed. A generally applicable model for distributions of lattice defects and their distortion fields is presented.

Acta Cryst. (1996). A52, 748-756 [ doi:10.1107/S010876739600596X ]

Evaluation of Sternheimer Nuclear Quadrupole Shielding Functions and their Application to the Determination of the ⁵⁷Fe^m Nuclear Quadrupole Moment from X-ray-Determined Charge Densities

Z. Su and P. Coppens

Synopsis: Values for the electric field gradient at the iron nucleus from the X-ray charge density and from Mössbauer spectroscopy are compared to obtain the ⁵⁷Fe^m nuclear quadrupole moment. Sternheimer shielding and antishielding factors are derived and used to account for core-polarization effects.

Acta Cryst. (1996). A52, 757-765 [ doi:10.1107/S0108767396006538 ]

The Use of Discrete Hilbert Transforms in Phase Extension and Improvement

G. Zanotti, F. Fogale and G. Capitani

Synopsis: A model-independent procedure for phase extension and improvement, based on the discrete Hilbert transforms, is presented.

Acta Cryst. (1996). A52, 766-769 [ doi:10.1107/S010876739609993X ]

Optical Activity of Crystalline Glutamic Acids

T. Asahi, H. Utsumi, Y. Itagaki, I. Kagomiya and J. Kobayashi

Synopsis: As the first study on gyro-optical properties of amino acids, temperature dependences of gyration tensor components of L- and D-glutamic acids were measured using the high-accuracy universal polarimeter (HAUP).

Acta Cryst. (1996). A52, 770-781 [ doi:10.1107/S0108767396005697 ]

Atomic Dispacement Parameter Nomenclature. Report of a Subcommittee on Atomic Displacement Parameter Nomenclature

K. N. Trueblood, H.-B. Bürgi, H. Burzlaff, J. D. Dunitz, C. M. Gramaccioli, H. H. Schulz, U. Shmueli and S. C. Abrahams

Synopsis: The nomenclature and symbols to be used in discussing the parameters that describe dynamic and static displacements of atoms in crystals, as determined from Bragg diffraction data, are considered in detail. The emphasis is on parameters derived from the Gaussian approximation.

short communications

Acta Cryst. (1996). A52, 782-784 [ doi:10.1107/S010876739600548X ]

Combined molecular replacement

L. Tong

Synopsis: The combined molecular replacement protocol performs a limited six-dimensional search to find molecular replacement solutions.

letters to the editor

Acta Cryst. (1996). A52, 785 [ doi:10.1107/S0108767396005703 ]

Comments on Crystal Properties via Group Theory by A. S. Nowick, Cambridge University Press, 1995

J. F. Nye

international union of crystallography

Acta Cryst. (1996). A52, 786 [ doi:10.1107/S0108767396099928 ]