Computational study of the energy landscape of water on the ThO2 {111} surface

The bulk and surface properties of ThO2 are studied computationally using density functional theory within the LSDA+U approach. The computational method is benchmarked against bulk lattice parameter and band gap, the best combined description of which is with the PBE functional and the Liechtenstein method with U = 7 and J = 1, and without spin orbit coupling. The optimised computational settings are used to study the reaction of water with the {111} surface, which we find to be hydrophilic. Molecular adsorption of a single water molecule is energetically favourable, and dissociation of this water to form surface hydroxyl groups is barrierless. This wetted surface can aid further water adsorption, with an even lower free energy difference than the first adsorption, although dissociation of the second water is much harder than the first. Reaction of H+, H. radical or OH- groups with the wetted {111} surface has a substantial energy barrier, and reaction with H+ is very sensitive to temperature.