First-principles study of the interaction of oxygen with the SnO2(1 1 0) surface

First-principles calculations based on density functional theory in the generalised gradient approximation, together with pseudopotentials and plane-wave basis sets, have been used to investigate the energetics of oxygen adsorption on stoichiometric and weakly and strongly reduced SnO2(1 1 0) surfaces. It is shown that, if the surface species formed by oxygen adsorption are restricted to be charge neutral, then oxygen cannot be exothermically adsorbed from the gas phase on the stoichiometric surface. A variety of molecular and dissociative modes of adsorption are examined on the reduced surface produced by removing all bridging oxygens and on the weakly reduced surface that results from removal of only a fraction of these oxygens, with the adsorbed species being in both the singlet and the triplet states, and we identify a number of modes not discussed before in the literature. We use the calculated adsorption energies to propose a tentative assignment of these adsorption modes to the peaks observed in temperature programmed desorption experiments on the SnO2 and TiO2(1 1 0) surfaces.