Multiple Water Layers on AnO₂ {111}, {110} and {100} Surfaces (An = U, Pu); A Computational Study

The geometries and energies of adsorption of up to five layers of water on the {111}, {110}, and {100} surfaces of stoichiometric UO₂ and PuO₂ are studied computationally with Hubbard U-corrected density functional theory within the periodic boundary condition framework. This work builds on their recent study of the surface-bound water monolayers [Tegner et al., J. Phys. Chem. C 121, 1675 (2017)], and the water geometries within this first layer are used as the starting point for the present calculations. Significant variations are found in the per-layer adsorption energies, as a result of differing extents of intra- and interlayer hydrogen bonding. After the adsorption of several additional layers, the effect of the surface-bound water geometries diminishes, and the average adsorption energy per water molecule is ca. 0.5–0.6 eV (similar to that in bulk water), irrespective of the surface.