RELAXATION AND RUMPLING MECHANISMS ON OXIDE SURFACES

We associate a self-consistent electronic structure calculation with a conjugate gradient technique for geometry optimization, to study stru ctural distortions on stoichiometric oxide surfaces. We discuss the re laxation and rumpling effects and their consequences on the surface el ectronic structure in a series of three MgO surfaces: (100), (110), (2 11) characterized by an increasing number of broken bonds, on the (110 ) faces of rocksalt oxides presenting various ionic characters: MgO, C aO, SrO and BaO, and on two non-polar rutile TiO2 faces: (110) and (00 1). The numerical results are interpreted in the framework of an analy tical model and the competition between covalent and electrostatic eff ects is investigated. A new mechanism of rumpling on oxide surfaces is proposed.