Nonsymmetrical X-ray diffraction in a perfect rectangular t × l crystal. Extinction and absorption

Nonsymmetrical diffraction in a perfect rectangular t × l crystal is analysed using the Takagi–Taupin equations. Analytical and numerical results are presented for the extinction and absorption factors..

Temperature-dependent X-ray dynamical diffraction: Darwin theory simulations

Darwin theory is used for computer simulations of diffraction from perfect Si and Ge crystals with thermal vibrations. Dynamical theory with a Debye–Waller factor fits most results, but deviations at high temperature call into question the usual quasi-ergodic hypothesis.

Resonant X-ray diffraction in incommensurately modulated crystals. Symmetry consideration of anisotropic anomalous scattering

It is shown that the additional ATS main reflections and ATS satellites can appear in the diffraction pattern of an incommensurately modulated crystal when the wavelength of the incident X-radiation is close to the absorption edge.

Influence of intermolecular interactions on multipole-refined electron densities

Model X-ray data are computed from a superposition of ab initio molecular electron densities in the crystal, as well as from periodic crystal Hartree–Fock electron densities, for several hydrogen-bonded systems and the weakly bound acetylene. Interaction effects on the electron density are illustrated and retrieved quantitatively by suitable multipole models. Multipole refinement reveals enhancement of the molecular dipole moment for hydrogen-bonded crystals but negligible change in molecular second moments. Electric field gradients at H nuclei are also discussed.

The periodic average structure of particular quasicrystals

Particular quasiperiodic structures with non-crystallographic symmetry exhibit discrete periodic average structures. Examples for one-, two- and three-dimensional quasiperiodic structures are discussed.

Minimal surfaces with self-intersections along straight lines. I. Derivation and properties

A new procedure for the derivation of minimal surfaces with self-intersections along straight lines is introduced. The deduction of several properties of each such surface from its generating polygon is described.

Comments on the characteristics of incommensurate modulation in quartz: discussion about a neutron scattering experiment

From the analysis of the elastic neutron scattering data by Dolino et al. [J. Phys. (Paris) (1984), 45, 361–371]>, it is shown that in the incommensurate (IC) phase of quartz there exists a strong component of the acoustic displacements of the modulation. The existence of a large is not consistent with the currently accepted model and a new model is needed in order to understand the origin of the IC modulation in quartz.

A multisolution method of phase determination by combined maximization of entropy and likelihood. VI. The use of error-correcting codes as a source of phase permutation and their application to the phase problem in powder, electron and macromolecular crystallography

Error-correcting codes are used to permute phases in a maximum-entropy–likelihood environment. The method is applied to powder, electron diffraction and protein data.

On the prediction of crystal morphology. III. Equilibrium and growth behaviour of crystal faces containing multiple connected nets

Using Monte Carlo simulations, the equilibrium and growth behaviour of crystal faces having more than one connected net are studied. The crystal habit is in such cases dependent on the supersaturation. Flat, rough and disordered flat phases are found.

A practical guide to phase retrieval and the reconstruction of analytic functions from measurements of their absolute values

Local structure from diffraction

International Union of Crystallography Acta Crystallographica Section A
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