Acta Crystallographica Section A

Foundations of Crystallography

Volume 68, Part 6 (November 2012)


	Cover illustration: The sequence of constructing the cartwheel pattern of the first-level hierarchy of the quasi-periodic pattern on the interior walls of the courtyard of the Madrasa of al-'Attarin (1323), Fez, Morocco [Al Ajlouni (2012). Acta Cryst. A68, 235-243].

feature articles
research papers
addenda and errata
book reviews
international union of crystallography

feature articles

Acta Cryst. (2012). A68, 667-674 [ doi:10.1107/S0108767312033715 ]

Fifty years of aperiodic crystals

Synopsis: In the 1960s the first examples were found of crystals which were not lattice periodic but quasiperiodic (a more general notion), contradicting the prevailing idea that crystals should be lattice periodic. The most interesting class of these aperiodic crystals was that of quasicrystals, discovered in 1982 by Dan Shechtman. A brief history of the development of the field of aperiodic crystals is given.

Online 18 September 2012

research papers

Acta Cryst. (2012). A68, 675-686 [ doi:10.1107/S0108767312031996 ]

Experimental determination of spin-dependent electron density by joint refinement of X-ray and polarized neutron diffraction data

M. Deutsch, N. Claiser, S. Pillet, Y. Chumakov, P. Becker, J.-M. Gillet, B. Gillon, C. Lecomte and M. Souhassou

Synopsis: An algorithm for joint multipolar charge and spin refinement against X-ray and polarized neutron diffraction data is described and applied for the first time to molecular magnetic crystals. This algorithm is implemented in the software MOLLYNX.

Online 18 September 2012

Acta Cryst. (2012). A68, 687-702 [ doi:10.1107/S0108767312031832 ]

Keyhole electron diffractive imaging (KEDI)

L. De Caro, E. Carlino, F. A. Vittoria, D. Siliqi and C. Giannini

Synopsis: Keyhole electron diffractive imaging is a new technique for imaging the structure of a crystalline specimen at sub-ångström resolution with a transmission electron microscope. The method is demonstrated by simulations and experiments.

Online 7 September 2012

Acta Cryst. (2012). A68, 703-704 [ doi:10.1107/S010876731203200X ]

Expectation values for integer powers of a Poisson-distributed random number

J. Henn

Synopsis: Expectation values of a Poisson-distributed random number are derived for the well known positive integer powers and for as yet not known negative integer powers.

Online 7 September 2012

Acta Cryst. (2012). A68, 705-714 [ doi:10.1107/S010876731203317X ]

Is it possible to derive quantitative information on polarization of electron density from the multipolar model?

J. M. Bak, Z. Czyznikowska and P. M. Dominiak

Synopsis: Tests were carried out to determine whether the Hansen-Coppens multipolar model is accurate enough to study changes of electrostatic properties under the influence of a crystal field. The study revealed that electrostatic properties obtained from the multipolar model are significantly different from those obtained from theoretical cluster or perturbation theory calculations.

Online 25 September 2012

Acta Cryst. (2012). A68, 715-728 [ doi:10.1107/S0108767312034010 ]

A critical analysis of dipole-moment calculations as obtained from experimental and theoretical structure factors

A. Poulain-Paul, A. Nassour, C. Jelsch, B. Guillot, M. Kubicki and C. Lecomte

Synopsis: Three charge-density models were tested against theoretical and experimental X-ray diffraction data and the resulting molecular dipole moments are compared.

Online 5 October 2012

Acta Cryst. (2012). A68, 729-735 [ doi:10.1107/S0108767312034319 ]

Dynamical diffraction effect in a curved multi-plate crystal cavity

Y.-Y. Chang, Y.-W. Tsai, Y.-H. Wu, M.-T. Tang and S.-L. Chang

Synopsis: In order to investigate the focusing behavior in a curved multi-plate crystal cavity under the back-diffraction condition, a modified algorithm for X-ray dynamical diffraction theory is presented.

Online 5 October 2012

Acta Cryst. (2012). A68, 736-749 [ doi:10.1107/S0108767312034885 ]

Analysing Friedel averages and differences

S. Parsons, P. Pattison and H. D. Flack

Synopsis: The use of Friedel averages and differences is described for the following operations: determining whether a crystal is centrosymmetric or not, determining the point group of a crystal and validating intensity data after structure solution.

Online 18 October 2012

Acta Cryst. (2012). A68, 750-762 [ doi:10.1107/S0108767312037269 ]

Maximum-entropy-method charge densities based on structure-factor extraction with the commonly used Rietveld refinement programs GSAS, FullProf and Jana2006

N. Bindzus and B. B. Iversen

Synopsis: Synchrotron powder X-ray diffraction data are analysed with generally available Rietveld refinement software and strategies are suggested for subsequent calculation of maximum-entropy-method charge densities.

Online 18 October 2012

Acta Cryst. (2012). A68, 763-777 [ doi:10.1107/S010876731203615X ]

Orthorhombic sphere packings. IV. Trivariant lattice complexes of space groups without mirror planes belonging to crystal class mmm

H. Sowa

Synopsis: All homogeneous sphere packings were derived that refer to the trivariant orthorhombic lattice complexes of the space groups without mirror symmetry belonging to crystal class mmm.

Online 18 October 2012

Acta Cryst. (2012). A68, 778-779 [ doi:10.1107/S0108767312039505 ]

Absorption correction A* for cylindrical and spherical samples with extended range and high accuracy calculated by the Thorkildsen and Larsen analytical method

H.-C. Hu, C. Yang and K. Zhao

Synopsis: The absorption correction A* for cylindrical and spherical samples over the extended ranges of 0 [less-than or equal to] [mu] R 30 and 0 [theta] 90° and with high accuracy is calculated by the Thorkildsen and Larsen analytical method.