Using the ab initio total energy method based on the gradient-corrected local density approximation we have modeled the experimentally observed ( $3\times 2$) water monolayer on the MgO (100) surface. The lateral interactions between the adsorbed water molecules, the formation of hydrogen bonds, and the resulting strong dimerization of the adsorbate promote the dissociation of two out of six water molecules in the surface unit cell. Although, on the theoretical grounds, water dissociation on a defective MgO surface has been already reported, this is the first theoretical evidence of water dissociation on the perfect MgO (100) surface.

• Received 27 March 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.1271