Water adsorption and dissociation on SrTiO3(001) revisited: A density-functional theory study

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 hydroxilation 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 towards higher coverages.