ROLE OF ORIENTATION IN ACID OR ALKALINE S TRENGTH OF SIMPLE OXIDE SURFACE SITES

The acid or basic strength of simple oxyde surface sites is characteri zed by the value of proton or hydroxyl group adsorption energies, calc ulated thanks to a self consistent tight binding method, in which elec tron-electron interactions are treated at a Hartree-Fock level. To exa mplify the role of the surface site environment, we present results ob tained on MgO in various geometries: planar surfaces with three differ ent orientations and clusters. We compare our results with predictions of electrostatic models. In addition, we discuss the modifications of the acid strength of a surface cation and of the basic strength of su rface oxygens, in different chemical environments, through a compariso n of the TiO2 faces of rutil (110) or SrTiO3 (100) and the SrO faces o f SrO (100) or SrTiO3 (100).