The energetics and structure of oxygen vacancies on the SnO2(110) surface

First-principles calculations based on density-functional theory, ultra-sof t pseudopotentials and plane-wave basis sets are used to investigate the en ergetics, relaxed ionic positions and electronic structure of oxygen vacanc ies on the SnO2(110) surface. We study three types of vacancy, obtained by removing bridging, in-plane and sub-bridging oxygen atoms, and calculations are made for a range of vacancy. concentrations, and for different geometr ies at some concentrations, in order to probe interactions between the vaca ncies. At low and intermediate concentrations, we find that the bridging va cancy is most stable, in agreement with experiment. At high concentrations, corresponding to a strongly reduced surface, the formation energies of bri dging and in-plane vacancies are almost the same, so that both types should occur in thermal equilibrium. In all situations examined, the relaxation o f ions surrounding the vacancies is small - typically 0.1 Angstrom or less. We present results showing how the electronic density of states in the gap region is affected by the different kinds of defects, and we discuss the r elation with measured ultraviolet photoelectron spectra. (C) 2000 Elsevier Science B.V. All rights reserved.