Theoretical investigation of hydroxylated oxide surfaces

A self-consistent electronic structure calculation, in the slab geometry, is performed to model the dissociative adsorption of water on several oxide surfaces in the limit of complete saturation. We discuss the adsorption characteristics along a series of oxides presenting a growing acidity: BaO, SrO, CaO, MgO, TiO₂, and SiO₂, and on three MgO surfaces: (100), (110), and (211) on which the atoms have different environments. Special emphasis is borne on the charge transfers, the densities of states and the oxide gap modification upon hydroxylation. We show that these quantities are dependent upon the coverage and that unstable MgO surfaces are more reactive towards water dissociation. Finally, by optimizing the geometry on the three MgO surfaces, we discuss the link between the electronic and structural degrees of freedom on hydroxylated surfaces.