Mixed Molecular and Dissociative Water Adsorption on MgO[100]

First principles molecular dynamics (MD) simulations, of water adsorption on the $\mathrm{MgO}\left[100\right]$ surface, was performed to determine the molecular structure and chemical nature of the adsorbed water at varying coverage. Dissociative adsorption was stabilized by hydrogen bond donation from neighboring water molecules. The dissociation barrier had a strong dependence on coverage. Spontaneous dissociation was observed in picosecond MD simulations above 1/2 monolayer (ML) coverage. Ordered structures with $c[3\times 2]$ symmetry were examined at 2/3 and 1 ML coverage. The ordered $c[3\times 2]$ phase consisted of a mixture of dissociated and molecular adsorbed molecules.