A computer program designed to provide a number of quantitative analysis tools for high-resolution imaging and electron diffraction data is described. The program includes basic image manipulation, both real space and reciprocal space image processing, Wiener-filtering, symmetry averaging, methods for quantification of electron diffraction patterns and two-dimensional direct methods. The progra...

A brief review is given of the status of crystallographic direct methods for solving surface structure problems. The basic concepts of using the a priori information that the scattering comes from atoms to generate self-consistent equations and statistical constraints upon the phases are described. The use of a genetic algorithm to perform a search over possible phases is then discussed. Finall...

Recent work has demonstrated that direct methods, using the minimum relative entropy approach, can be applied to strongly dynamical diffraction from bulk inorganic structures. In the present work, the possibility of using intensity data which is thickness averaged, as for a wedge-shaped specimen, is explored. It is shown that for structures which contain a large number of light atoms, well reso...

In the most developed branches of crystallography, structure solution proceeds by two distinct steps: first, an approximate model of the structure is deduced directly from the measured data by an algorithm which assumes no preconceived model; second, a process of structure refinement simulates the experimental data for systematic variations of the parameters of such a model and determines a fin...

The electron density function, Q(r), in a crystal determines its diffraction pattern, i.e. both the magnitudes and phases of its x-ray diffraction maxima, and conversely. If, however, as is always the case, only magnitudes are available from the diffraction experiment, then the density function ρ(r) cannot be recovered. If one invokes prior structural knowledge, usually that the crystal is comp...