Adsorption of Au atoms on stoichiometric and reduced TiO₂(1 1 0) rutile surfaces: A first principles study

Using ab initio quantum mechanical methods (DFT-GGA/LDA, pseudopotentials) we have investigated the adsorption properties of Au atoms on stoichiometric and reduced TiO₂(110) rutile surfaces. This study predicts that the most stable adsorption site for the Au atom on the stoichiometric surface is on the fourfold hollow position over the fivefold-coordinated Ti and in-plane and bridging O atoms, indicated as the H2 site. At the H2 site, it is likely that the covalent and ionic bonding interactions with the fivefold-coordinated Ti and the bridging O, respectively, contribute synergistically to the Au adsorption. For Au adsorption over a neutral F_s⁰ center on the reduced surface, there is rather strong ionic bonding between the Au and surrounding sixfold-coordinated Ti atoms. The Au adsorption energy at the defect site is affected significantly by the presence of oxygen vacancies nearby along the [001] direction. Our DFT-GGA results clearly show that the binding of Au to an oxygen vacancy site is substantially stronger than to the stoichiometric surface.