Acta Crystallographica Section A

Foundations of Crystallography

Volume 52, Part 4 (July 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.

lead articles
topical reviews
research papers
short communications

lead articles

Acta Cryst. (1996). A52, 509-560 [doi:10.1107/S0108767396000967]

Crystallography of Quasiperiodic Crystals

A. Yamamoto

Synopsis: A unified description is given of modulated crystals and quasicrystals based on higher-dimensional crystallography.

topical reviews

Acta Cryst. (1996). A52, 561-589 [doi:10.1107/S0108767396001560]

Maximum Entropy and Bayesian Statistics in Crystallography: a Review of Practical Applications

C. J. Gilmore

Synopsis: The applications of the maximum entropy and Bayesian methods to problems in X-ray, neutron and electron crystallography are reviewed.

research papers

Acta Cryst. (1996). A52, 590-595 [doi:10.1107/S0108767396000785]

Growth and Polytype Transformation of AgI-Doped and Undoped PbI₂ Crystals

A. Jain and G. C. Trigunayat

Synopsis: Significant results on (a) polytype formation in undoped and AgI-doped single crystals of lead iodide and (b) polytype transformation in them on prolonged storage of several months are reported and analysed.

Acta Cryst. (1996). A52, 596-605 [doi:10.1107/S0108767396001171]

The Symmetry of Three-Beam Scattering Equations: Inversion of Three-Beam Diffraction Patterns from Centrosymmetric Crystals

A. F. Moodie, J. Etheridge and C. J. Humphreys

Synopsis: It is shown that, for a centrosymmetric crystal and within the range of validity of the three-beam approximation, the phases as well as the magnitudes of the three structure amplitudes can be measured uniquely and directly from the geometry of the intensity distributions in the discs of a convergent-beam diffraction pattern. Separate proofs are given in terms of Lie groups, Dirac projector operators and Bloch waves.

Acta Cryst. (1996). A52, 606-613 [doi:10.1107/S0108767396001845]

MEM Analysis of Electron-Density Distributions for Silicon and Diamond using Short-Wavelength X-rays (W K 1)

K. Yamamoto, Y. Takahashi, K. Ohshima, F. P. Okamura and K. Yukino

Synopsis: The electron-density distributions of silicon and diamond with high resolution were synthesized by the maximum-entropy method using short-wavelength X-rays (W K [alpha] 1).

Acta Cryst. (1996). A52, 614-620 [doi:10.1107/S0108767396000761]

X-ray Back-Diffraction Profiles with an Si (111) Plate

C. Cusatis, D. Udron, I. Mazzaro, C. Giles and H. Tolentino

Synopsis: An experimental study is presented of the profiles backward and forward diffracted by a thin Si (111) crystal plate using synchrotron radiation.

Acta Cryst. (1996). A52, 621-628 [doi:10.1107/S0108767396002243]

Position-Resolved Measurement of the Polarization State in the Forward-Diffracted X-ray Beam

W. Leitenberger, C. Eisenschmidt and H.-R. Höche

Synopsis: The polarization state inside the transmitted 0 beam in the Laue case of X-ray diffraction was determined with high local resolution. Calculations according to the dynamical theory were used to explain the experimental data.

Acta Cryst. (1996). A52, 629-633 [doi:10.1107/S0108767396002565]

Discrete Hilbert Transforms and the Phase Problem in Crystallography

A. F. Mishnev

Synopsis: By means of discrete Hilbert transforms, the autocorrelation function (the Patterson for a single unit cell) has been incorporated into the analysis of the crystallographic phase problem.

Acta Cryst. (1996). A52, 634-639 [doi:10.1107/S0108767396003285]

A Tangent Formula Derived from Patterson-Function Arguments. IV. The Solution of Difference Structures Directly from Superstructure Reflections

J. Rius, C. Miravitlles and R. Allmann

Synopsis: The direct-methods solution of the difference structure of a superstructure using only the intensities of superstructure reflections is shown. This result may be relevant for determining the internal structure of reconstructed surfaces by direct methods.

Acta Cryst. (1996). A52, 640-644 [doi:10.1107/S0108767396003479]

Direct Methods for Intergrowth Compounds. III. Solving the Average Structure in Multidimensional Space

Y.-D. Mo, Z. Fu, H. Fan, S. van Smaalen, E. J. W. Lam and P. T. Beurskens

Synopsis: A direct-methods procedure is presented for the determination of a composite crystal. The crucial step is the definition of normalized structure factors for the different reflection groups.

short communications

Acta Cryst. (1996). A52, 645-646 [doi:10.1107/S0108767396002516]

Novel regular quinquehedral packing obtained by the local approach

V. V. Manzhar

Synopsis: The derivation of novel regular three-dimensional packing with a square-pyramidal coordination polyhedron is briefly described within the local approach.

Acta Cryst. (1996). A52, 647-648 [doi:10.1107/S0108767396004151]

Optimizing bond lengths in a model using Patterson methods prior to the solution of the structure

C. C. Wilson

Synopsis: A method is described that allows the refinement of bond lengths in a partial model using Patterson-method calculations. The information has uses in fragment building prior to structure solution.