RELAXATION AND DYNAMICS OF THE (110) SURFACES OF THE CESIUM-CHLORIDE STRUCTURE CRYSTALS CSCL, CSBR AND CSI

We have treated the relaxation and the dynamics of the (110) surfaces of the cesium halogens CsCl, CsBr and CsI in the framework of shell models, in which the short range interactions are represented by Born-Mayer potentials. The relaxation in the surface layer is small (approximately 0.01a0) and diminishes rapidly away from the surface. The calculated normal vibrations of twenty-five layer slabs are presented in three-dimensional diagrams, which provide a very direct and pictorial display of the surface localization of vibrational states. For all three compounds a rich structure of surface modes and surface resonances is found, which is dependent on the amount of overlap of the bulk bands.