The Ab Initio Simulation of Molecular Processes on Oxide Surfaces

Ab initio calculations based on both density-functional theory (DFT) and Hartree-Fock (HF) methods are used to investigate the energetics and equilibrium structure of the stoichiometric and reduced TiO 2 (110) surface, the adsorption of potassium on the (100) surface and of water on the (110) surface. It is shown that DFT and HF predictions of the relaxed ionic positions at the stoichiometric surface agree well with each other and fairly well with recent x-ray diiraction measurements. The inclusion of spin polarisation is shown to have a major eeect on the energetics of the reduced surface formed by removal of bridging oxygens or by the adsorption of alkali metal overlay-ers. The gap states observed to be induced by reduction are not reproduced unless spin polarisation is included. Static and dynamic DFT calculations on adsorbed water on TiO 2 (110) connrm that dissociation of H 2 O leads to sta-bilisation at low coverages, but suggest a more complex picture at monolayer coverage, in which there is a rather delicate balance between molecular and 1 dissociated geometries.