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Abstract

We present a comprehensive density functional theory study addressing the adsorption, dissociation, and successive diffusion of water molecules on the two regular terminations of SrTiO₃(001). Combining the obtained supercell-geometry converged energetics within a first-principles thermodynamics framework we are able to reproduce the experimentally observed hydroxylation of the SrO-termination already at lowest background humidity, whereas the TiO₂-termination stays free of water molecules in the regime of low water partial pressures. This different behavior is traced back to the effortless formation of energetically very favorable hydroxyl-pairs on the prior termination. Contrary to the prevalent understanding our calculations indicate that at low coverages also the less water-affine TiO₂-termination can readily decompose water, with the often described molecular state only stabilized toward higher coverages.