APPLICATIONS OF XD IN CHARGE DENSITY RESEARCH. T. Koritsanszky Institute for Crystallography, Free University of Berlin, Germany

An introduction to XD /1/, a Computer Program Package for Multipole Refinement and Analysis of Electron Densities from Diffraction Data, will be given. This new package is under development, within an IUCr project, and test versions have been available for the wide scientific community. The method of extracting electronic properies from Bragg reflections is based on precise X-ray diffraction data and non-conventional scattering formalis /2/. The procedure, due to the approximations involved, has limitations and the evaluation of the results, obtainable almost automatically, needs expertise. The lecture intends to help the "non-experts" to get familiar with the basic aspects of the method and the main features of the different programs. A general refinement strategy applicable almost routinely will be proposed with the emphasis also on testing the parameter etimates obtained. Examples will be given when constrained refinements increased the physical significance of the result. Several applications including full topological analysis of experimental electron densities and Laplacian functions will be presented.

/1/ T. Koritsanszky, S. Howard, P.R. Mallinson, Z. Su, T. Richter and N.K. Hansen: XD a Computer Program Package for Multipole Refinement and Analysis of Electron Densities from Diffraction Data, 1995.

/2/ N.K. Hansen and P. Coppens, Acta Cryst. A34, 909, 1978.