AB-INITIO SIMULATION OF MOLECULAR PROCESSES ON OXIDE SURFACES

Ab initio calculations based on both density functional theory (DFT) a nd Hartree-Fock (HF) methods are used to investigate the energetics an d equilibrium structure of the stoichiometric and reduced TiO2 (110) s urface, 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 r elaxed ionic positions at the stoichiometric surface agree well with e ach other and fairly well with recent X-ray diffraction measurements. The inclusion of spin polarisation is shown to have a major effect on the energetics of the reduced surface formed by removal of bridging ox ygens. The gap states observed to be induced by reduction are not repr oduced unless spin polarisation is included. Static and dynamic DFT ca lculations on adsorbed water on TiO2 (110) confirm that dissociation o f H2O leads to stabilisation at low coverages, but suggest a more comp lex picture at monolayer coverage, in which there is a rather delicate balance between molecular and dissociated geometries.