Acta Crystallographica Section A

Foundations of Crystallography

Volume 52, Part 3 (May 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.

obituaries
topical reviews
research papers
short communications
international union of crystallography
books received

obituaries

Acta Cryst. (1996). A52, 329-330 [doi:10.1107/S0108767396001869]

Y. T. Struchkov, 1926-1995

A. Kálmán

topical reviews

Acta Cryst. (1996). A52, 331-339 [doi:10.1107/S0108767395013651]

Direct Methods and Powder Data: State of the Art and Perspectives

C. Giacovazzo

Synopsis: The various problems that have to be faced when direct phasing procedures are applied to powder data are described.

research papers

Acta Cryst. (1996). A52, 340-348 [doi:10.1107/S010876739501539X]

Planar Facet Interface: Overlapping Volume and Scherrer Constant Expressions

S. Ciccariello and R. Sobry

Synopsis: For a powder sample, the overlap function is a cubic function when the interface consists of planar facets. The explicit expressions of the Scherrer constants are reported.

Acta Cryst. (1996). A52, 349-364 [doi:10.1107/S0108767395015522]

Molecular Geometry of Incommensurate Structures

W. Paciorek, V. Bussien Gaillard, K. Schenk and G. Chapuis

Synopsis: Molecular geometry calculations in the superspace framework of incommensurate structure analysis are presented in detail.

Acta Cryst. (1996). A52, 365-368 [doi:10.1107/S0108767395015868]

The Map Correlation Coefficient for Optimally Superposed Maps

V. Yu. Lunin and N. L. Lunina

Synopsis: The comparison of ab initio generated phase sets requires preliminary map alignment. A space-group-symmetry-specific algorithm for optimal origin and enantiomorph choices is proposed.

Acta Cryst. (1996). A52, 369-378 [doi:10.1107/S0108767395015832]

Anharmonic Motion vs Chemical Bonding: on the Interpretation of Electron Densities Determined by X-ray Diffraction

R Restori and D. Schwarzenbach

Synopsis: Anharmonic motions and effects of chemical bonding of heavy atoms result in nearly identical features of difference electron-density maps, which vary similarly with temperature except at very low temperatures. Examples are K₂PtCl₆ and Si.

Acta Cryst. (1996). A52, 379-384 [doi:10.1107/S0108767395015893]

A Relativistic n-Beam Dynamical Theory for Fast Electron Diffraction

K. Watanabe, S. Hara and I. Hashimoto

Synopsis: From the Dirac equation with periodic scalar potential, an n-beam dynamical formula of high-energy diffraction by a crystal is developed by the matrix representation.

Acta Cryst. (1996). A52, 385-390 [doi:10.1107/S0108767395016886]

On Integrating the Techniques of Direct Methods with Anomalous Dispersion: the One-Phase Structure Seminvariants in the Tetragonal System

D. Velmurugan, L. Govindasamy and K. K. Geetha

Synopsis: Traditional direct methods are combined with anomalous scattering techniques for their potential applications to mediun/large molecules.

Acta Cryst. (1996). A52, 391-396 [doi:10.1107/S0108767395016953]

The Double Shear Geometry and Associated Rational Orientational Relationships

L. Beraha and M. Duneau

Synopsis: A new classification of coincidence lattices is derived from the factorization of transition matrices into a product of shear transformations.

Acta Cryst. (1996). A52, 397-407 [doi:10.1107/S0108767395017132]

The Two-Channel Maximum-Entropy Method Applied to the Charge Density of a Molecular Crystal: -Glycine

R. J. Papoular, Y. Vekhter and P. Coppens

Synopsis: As the effects of chemical bonding are small compared to the dynamic range of the total density, the two-channel maximum-entropy method is applied to the deformation density of [alpha] -glycine. The molecular dipole moment is reasonably well preserved in the reconstruction provided a non-uniform informative prior density is used.

Acta Cryst. (1996). A52, 408-412 [doi:10.1107/S0108767395017144]

The Crystal Structure and Optical Activity of Tellurium

P. J. Brown and J. B. Forsyth

Synopsis: The Schwinger scattering of neutrons has been used to determine the sense of rotation of the helices of atoms in a crystal of tellurium. Its optical activity shows that the rotation of the plane of polarization of infrared radiation traversing the crystal parallel to the triad axis is in the same sense as the rotation of the helices.

Acta Cryst. (1996). A52, 413-418 [doi:10.1107/S0108767395017181]

Theoretical Structure Factors and Electron Density of Magnesite(MgCO₃)

M. Catti and A. Pavese

Synopsis: Theoretical structure factors F_q of rhombohedral magnesite (MgCO₃) have been computed by quantum-mechanical periodic Hartree-Fock methods and compared with observed |F_o| (literature data) and conventional F_c (independent-spherical-atom model) values. Difference electron-density maps have been calculated on the most important sections.

Acta Cryst. (1996). A52, 419-426 [doi:10.1107/S0108767396000177]

New Developments in Direct Shape Determination from Small-Angle Scattering. 2. Uniqueness

D. I. Svergun, V. V. Volkov, M. B. Kozin and H. B. Stuhrmann

Synopsis: The low-resolution shape restoration from small-angle scattering data is shown to be unique if the number of shape parameters is 1 to 1.5 times the number of Shannon channels covered by the data set.

Acta Cryst. (1996). A52, 427-437 [doi:10.1107/S010876739600075X]

The Non-Resonant Magnetic X-ray Scattering Cross Section of MnF₂. 1. Medium X-ray Energies from 5 to 12keV

T. Brückel, M. Lippert, T. Köhler, J. R. Schneider, W. Prandl, V. Rilling and M. Schilling

Synopsis: A new set-up for magnetic X-ray diffraction is described and the form of the non-resonant magnetic X-ray scattering cross section is investigated for the model system MnF₂.

Acta Cryst. (1996). A52, 438-449 [doi:10.1107/S0108767396000773]

The Non-Resonant Magnetic X-ray Scattering Cross Section of MnF₂. 2. High-Energy X-ray Diffraction at 80keV

J. Strempfer, T. Brückel, U. Rütt, J. R. Schneider, K.-D. Liss and T. Tschentscher

Synopsis: A new method for the microscopic investigation of magnetic materials, namely the non-resonant diffraction of high-energy X-rays (E > 80 keV), is discussed and experimental results for MnF₂ are reported.

Acta Cryst. (1996). A52, 450-455 [doi:10.1107/S0108767396001432]

Corrections to Atomic Scattering Factors for High-Energy Electrons Arising from Atomic Vibrations

G. R. Anstis

Synopsis: The potential used to calculate electron diffraction intensities depends on the amplitudes of atomic vibrations. This paper provides a method for calculating this potential.

Acta Cryst. (1996). A52, 456-470 [doi:10.1107/S010876739600089X]

Debye-Waller Factors and Absorptive Scattering Factors of Elemental Crystals

L.-M. Peng, G. Ren, S. L. Dudarev and M. J. Whelan

Synopsis: Debye-Waller factors are given for 66 elemental crystals and absorptive scattering factors are given for 44 elemental crystals over the temperature range 1 to 1000 K.

Acta Cryst. (1996). A52, 471-475 [doi:10.1107/S010876739600116X]

Dynamical RHEED Calculations from the Surface of a Semi-Infinite Crystal

L.-M. Peng, S. L. Dudarev and M. J. Whelan

Synopsis: A slab method is developed for dynamical RHEED calculations from the surface of a semi-infinite crystal.

Acta Cryst. (1996). A52, 476-479 [doi:10.1107/S0108767396001110]

The Locked Translation Function and Other Applications of a Patterson Correlation Function

L. Tong

Synopsis: A Patterson correlation function has been used to define a locked translation function and to refine rotational parameters of a search atomic model.

Acta Cryst. (1996). A52, 480-489 [doi:10.1107/S0108767396001420]

Direct Phasing in Protein Electron Crystallography - Phase Extension and the Prospects for Ab Initio Determinations

D. L. Dorset

Synopsis: The Sayre equation is evaluated as a technique for phase extension or ab initio phase determination, using electron crystallographic data from a bacterial porin.

Acta Cryst. (1996). A52, 490-496 [doi:10.1107/S0108767396001237]

The SAS Maximal Principle: a New Approach to the Phase Problem

H. A. Hauptman

Synopsis: When single-wavelength anomalous acattering (SAS) diffraction intensities are available, the phase problem may be formulated as one in global optimization. This formulation permits a substantial strengthening of the traditional techniques of direct methods, particularly in the case that data are available at low resolution only.

short communications

Acta Cryst. (1996). A52, 497-498 [doi:10.1107/S0108767396000918]

Comment on Contrast of HOLZ lines in energy-filtered convergent-beam electron diffraction patterns from silicon by Lehmpfuhl, Krahl & Uchida (1995)

L. J. Allen and T. W. Josefsson

Synopsis: Contrary to statements in the recent literature, there is no evidence for strong anisotropy in the Debye-Waller factor for silicon at room temperature.

Acta Cryst. (1996). A52, 498-499 [doi:10.1107/S0108767395014553]

X-ray topography of a lysozyme crystal

V. Stojanoff and D. P. Siddons

Synopsis: White and monochromatic X-ray topographic methods are used to image defects in protein crystals.

international union of crystallography

Acta Cryst. (1996). A52, 500-501 [doi:10.1107/S0108767396099965]

International Tables for Crystallography Volume B. Corrigenda and Addenda to the First Edition (1993)

Acta Cryst. (1996). A52, 501-507 [doi:10.1107/S0108767396099953]

Keywords for the World Database of Crystallographers

books received

Acta Cryst. (1996). A52, 508 [doi:10.1107/S0108767396099941]