Acta Crystallographica Section A

Foundations of Crystallography

Volume 54, Part 4 (July 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
book reviews
books received

research papers

Acta Cryst. (1998). A54, 359-373 [doi:10.1107/S010876739701667X]

Beyond Space Groups: the Arithmetic Symmetry of Deformable Multilattices

M. Pitteri and G. Zanzotto

Synopsis: This paper presents an arithmetic approach to the symmetry of complex crystalline structures (multilattices). This generalizes the one classically used for simple lattices and gives a finer description of multilattice symmetry than that obtained through space groups.

Acta Cryst. (1998). A54, 374-387 [doi:10.1107/S0108767397018837]

Geometrical Model of the Phase Transformation of Decagonal Al-Co-Ni to its Periodic Approximant

M. Honal, T. Haibach and W. Steurer

Synopsis: A geometrical model of the quasicrystal-to-crystal transformation based on small atomic displacements including phason flips is discussed using the example of decagonal Al-Co-Ni.

Acta Cryst. (1998). A54, 388-398 [doi:10.1107/S0108767398003560]

Obtaining the Crystal Potential by Inversion from Electron Scattering Intensities

L. J. Allen, T. W. Josefsson and H. Leeb

Synopsis: A method to obtain the crystal potential from the intensities of diffracted beams in high-energy electron diffraction is proposed.

Acta Cryst. (1998). A54, 399-410 [doi:10.1107/S010876739701787X]

The Background: from Observation to a `Non-Event' in Single-Crystal Diffractometry

S. T. Maes, C. Vanhulle and A. T. H. Lenstra

Synopsis: Background intensities are summarized in a model defining an accurate reference level upon which the coherent Bragg intensities are superimposed. The background model reduces the random errors on I net eliminating the background as an error component.

Acta Cryst. (1998). A54, 411-415 [doi:10.1107/S0108767397019442]

Dynamical Three-Beam Diffraction in a Quasicrystal

Y. Zhang, R. Colella, Q. Shen and S. W. Kycia

Synopsis: A three-beam diffraction experiment is described in which circularly polarized X-rays are used. Different azimuthal plots are observed when the helicity of the incident beam is switched, in accordance with a noncentrosymmetric structure.

Acta Cryst. (1998). A54, 416-429 [doi:10.1107/S0108767397020278]

Symmetrical X-ray Diffraction in a Perfect Rectangular × l Crystal. Extinction and Absorption

G. Thorkildsen and H. B. Larsen

Synopsis: The Takagi-Taupin equations for two beams are analysed using the boundary-value Green function technique for the case of symmetrical diffraction in a perfect rectangular × l crystal. Analytical and numerical results are presented for the extinction and absorption factors.

Acta Cryst. (1998). A54, 430-437 [doi:10.1107/S0108767397016164]

Crystallogeometrical Approach to Stacking-Fault Analysis in Ordered Alloys

S. V. Dmitriev, A. M. Wusatowska-Sarnek, M. D. Starostenkov, A. N. Belyakov, T. Shigenari and T. Sakai

Synopsis: The analytical expression for the energy of an unrelaxed stacking fault in a n-dimensional ordered alloy is given in terms of the pair-potential functions.

Acta Cryst. (1998). A54, 438-446 [doi:10.1107/S0108767398000063]

The Ab Initio Solution of Structures from Powder Diffraction Data: the Use of Maximum Entropy and Likelihood to Determine the Relative Amplitudes of Overlapped Reflections Using the Pseudophase Concept

W. Dong and C. J. Gilmore

Synopsis: The maximum-entropy-likelihood method of solving crystal structures from powder diffraction data is extended to include the estimation of the individual intensities of the overlapping reflections using Duncan's statistical procedure combined with likelihood estimation.

Acta Cryst. (1998). A54, 447-451 [doi:10.1107/S0108767398000762]

Calculation of Thermodynamic Properties of Solids from Accurate Diffraction Data: Isotope Separation Factor in Systems Containing Crystalline Phase

R. P. Ozerov, A. V. Bochkarev, A. B. Sazonov, S. A. Samoilov and E. P. Magomedbekov

Synopsis: A method of calculation of the thermodynamic functions from accurate X-ray diffraction data has been developed. The isotope-reduced partition-function ratio [beta] D/H for the LiH (LiD) crystal and the separation factor [alpha] D/H for the isotope exchange in the solid-gas Li(H,D)-(H₂,D₂) system have been calculated.

Acta Cryst. (1998). A54, 452-459 [doi:10.1107/S0108767398000075]

A Two-Dimensional Bloch-Wave Method for Dynamical RHEED Calculations

K. Watanabe, S. Hara, Y. Horio and I. Hashimoto

Synopsis: A new two-dimensional Bloch-wave method is developed for dynamical RHEED calculations.

Acta Cryst. (1998). A54, 460-467 [doi:10.1107/S0108767398001457]

The `Frozen-Lattice' Approach for Incoherent Phonon Excitation in Electron Scattering. How Accurate Is It?

Z. L. Wang

Synopsis: For electron dynamic thermal diffuse scattering, it is proved for the first time that the calculation based on the `frozen lattice' model gives an identical result to the quantum inelastic phonon excitation theory if the incoherence between different orders of diffuse scattering is considered. This conclusion holds for both high- and low-energy electrons and it establishes the quantum-mechanical basis of many existing theories.

Acta Cryst. (1998). A54, 468-480 [doi:10.1107/S0108767398001548]

Relevance of Charge-Density Measurements for High-Precision Calculations

C. Petrillo, F. Sacchetti and G. Mazzone

Synopsis: The re-analysis of high-precision photon diffraction data in beryllium, diamond, silicon, copper and germanium is carried out for an accurate comparison with local density approximation calculations.

Acta Cryst. (1998). A54, 481-485 [doi:10.1107/S0108767398001901]

Electron Scattering Factors of Ions and their Parameterization

L.-M. Peng

Synopsis: Elastic electron scattering factors of 106 ions are represented in a parameterized form and it is shown that for most transmission electron diffraction applications the effect of crystal ionicity on the absorptive electron scattering may be neglected.

Acta Cryst. (1998). A54, 486-490 [doi:10.1107/S0108767398002669]

On the Relation of Modulated Structures with the Automorphisms of the d-Dimensional Tori Created by the Compaction of the (3+d)-Dimensional Space

P. Gusin and J. Warczewski

Synopsis: A hypothesis is put forward concerning the existence of the general relation between aperiodic crystal structures and the invariants of the group of the automorphisms of the d-dimensional torus. A relation is proved between the one-dimensional and two-dimensional displacive modulations and the rationality of some invariants of the group of automorphisms of both the circle S¹ and the torus T².

Acta Cryst. (1998). A54, 491-500 [doi:10.1107/S0108767397019806]

On the Prediction of Crystal Morphology. I. The Hartman-Perdok Theory Revisited

R. F. P. Grimbergen, H. Meekes, P. Bennema, C. S. Strom and L. J. P. Vogels

Synopsis: The Hartman-Perdok theory for the prediction of crystal morphology is reformulated on the basis of F faces having a roughening temperature higher than 0 K. The presence of multiple connected nets for a single orientation can give rise to symmetry roughening and high growth rates.

Acta Cryst. (1998). A54, 501-510 [doi:10.1107/S0108767397020357]

On the Prediction of Crystal Morphology. II. Symmetry Roughening of Pairs of Connected Nets

H. Meekes, P. Bennema and R. F. P. Grimbergen

Synopsis: All cases where symmetry may lead to symmetric roughening for pairs of connected nets of the crystal structure are derived. Symmetry roughening has severe implications for crystal morphology.

short communications

Acta Cryst. (1998). A54, 511-512 [doi:10.1107/S0108767398002657]

An exact analytical expression for the primary extinction factor for a perfect spherical crystal in the limit _oh /2

H. B. Larsen and G. Thorkildsen

Synopsis: An analytical formula is derived for the primary extinction factor in the Bragg limit in the case of a perfect spherical crystal. The result is compared with the corresponding Laue limit.

Acta Cryst. (1998). A54, 513-514 [doi:10.1107/S0108767398004176]

Compilation of temperature factors of hexagonal close packed elements

N. Gopi Krishna and D. B. Sirdeshmukh

Synopsis: A compilation of temperature factors for 14 h.c.p. elements is presented.

Acta Cryst. (1998). A54, 515 [doi:10.1107/S0108767398007284]

The equations of the statistical dynamical theory of X-ray diffraction for deformed crystals. Erratum

K. M. Pavlov and V. I. Punegov

Synopsis: Erratum to Acta Cryst. (1998), A54, 214-218.

book reviews

Acta Cryst. (1998). A54, 516 [doi:10.1107/S0108767397014499]

Simulations for solid state physics. An interactive teaching resource for students and teachers edited by R. H. Silsbee and J. Dräger

books received

Acta Cryst. (1998). A54, 516 [doi:10.1107/S010876739809998X]

Quantum dynamics of simple systems edited by G.-L. Oppo, S. M. Barnett, E. Riis and M. Wilkinson

Acta Cryst. (1998). A54, 516 [doi:10.1107/S0108767398099978]