November 2012 issue
Acta Cryst. (2012). A68, 667-674
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.
Acta Cryst. (2012). A68, 675-686
Experimental determination of spin-dependent electron density by joint refinement of X-ray and polarized neutron diffraction data
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.
Acta Cryst. (2012). A68, 687-702
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.
Acta Cryst. (2012). A68, 703-704
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.
Acta Cryst. (2012). A68, 705-714
Is it possible to derive quantitative information on polarization of electron density from the multipolar model?
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.
Acta Cryst. (2012). A68, 715-728
A critical analysis of dipole-moment calculations as obtained from experimental and theoretical structure factors
Three charge-density models were tested against theoretical and experimental X-ray diffraction data and the resulting molecular dipole moments are compared.
Acta Cryst. (2012). A68, 729-735
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.
Acta Cryst. (2012). A68, 736-749
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.
Acta Cryst. (2012). A68, 750-762
Maximum-entropy-method charge densities based on structure-factor extraction with the commonly used Rietveld refinement programs GSAS, FullProf and Jana2006
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.
Acta Cryst. (2012). A68, 763-777
Orthorhombic sphere packings. IV. Trivariant lattice complexes of space groups without mirror planes belonging to crystal class mmm
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.
Acta Cryst. (2012). A68, 778-779
Absorption correction A* for cylindrical and spherical samples with extended range and high accuracy calculated by the Thorkildsen and Larsen analytical method
The absorption correction A* for cylindrical and spherical samples over the extended ranges of 0 ≤ μR ≤ 30 and 0 ≤ θ ≤ 90° and with high accuracy is calculated by the Thorkildsen and Larsen analytical method.
addenda and errata
Acta Cryst. (2012). A68, 780
Acta Cryst. (2012). A68, 781-784
international union of crystallography
Acta Cryst. (2012). A68, 785
Acta Cryst. (2012). A68, 786-787