ELECTRON DENSITY AND PROPERTIES OF ROCK-SALT TYPE CRYSTALS V. E. Zavodnik^*, Yu. A. Abramov^#, A. I. Stash^*, E. L. Belokoneva^%, A. S. Avilov^**, U. Pietsch, J. Stahn,^& D. Feil^$, V. G. Tsirelson^#, ^*Karpov Institute of Physical Chemistry, Moscow, Russia; ^#Mendeleev University of Chemical Technology, Moscow, Russia; ^%Moscow State University, Moscow, Russia; ^**Institute of Crystallography, Moscow, Russia, & Potsdam University, Potsdam, Germany; ^$Twente University, Enschede, the Netherlands.

The X-ray diffraction studies of the electron density (ED) of the crys tals with rock-salt structure, traditional test crystals in solid state computational methods, should provide the basis for direct comparison of the theoretical and experimental data. However, the severe extinction and sometimes ignoring TDS distort the diffraction intensities and the problem of description of highly ionic electronic states exists in theore-tical calculations for these crystals. Therefore the reliable estimation of real today's level of both experimental and theoretical results concerned with electronic properties of these crystals is needed.

We have performed the accurate X-ray diffraction experiments and theoretical calculations by non-empirical Hartree-Fock method for LiF, NaF, NaCl and MgO crystals. In addition, the electron diffraction mea-surement of electrostatic potential in MgO was done. The quasi-static structure amplitudes reconstructed from the X-ray experiments were compared with theoretical ones calculated with different basis sets at experimental geometry. It was found that the extended optimised basis sets result to close agreement with experimental data, including low-angle "extinctional" reflections. The analysis of the ED (both experimental and theoretical) in terms of deformation density maps and Bader's quantum-topological theory was done. The electrostatic potential was calculated and compared with electron-diffraction data.

The support of this study by the Netherlands Organization for Scientific Research and Deutsche Forschungsgemeinschaft is acknowledged.