ELECTRON DENSITY DISTRIBUTION IN [[gamma]]-CuBr BY MAXIMUM ENTROPY METHOD. H. Ishibashi, J. Tamura and K. Nakahigashi, College of Integrated Arts and Sciences, Osaka Prefecture University, Sakai, Osaka 593, Japan

The electron density distribution of [[gamma]]-CuBr with sphalerite structure was determined by the maximum entropy method (MEM) with the aid of powder X-ray data at room temperature and 9 K. The electron density map of lower-density region for the ( 1 1 0) plane at room temperature is shown in figure. Covalent bonding between Cu and Br due to the strong admixture of Cu 3d and Br 4p states is clearly recognized. Further the valence electron density of Cu is elongated along the three directions indicated by arrows. These elongations originated from the anharmonic thermal motions. On the other hand, the thermal motions of both atoms were reduced at 9 K, particularly the spread of Cu along the arrows disappeared. The root mean square displacement of Cu and Br at room temperature and 9 K was 0.222 Å, 0.158 Å and 0.089 Å, 0.074 Å, respectively, and agreed well with those determined by the neutron diffraction studies (F. Altorfer et al., J. Phys.: Condens. Matter, 1994, 6,9949-9962).

Figure. The MEM map of [[gamma]]-CuBr for the ( 1 1 0) plane at room temperature. Contour lines (eÅ^-3) are drawn from 0.3 to 2.1 with 0.2 intervals.