The structure and spectroscopy of monolayers of water on MgO: An ab initiostudy

The structure and energetics of a monolayer of water on a perfect MgO subst rate is investigated by ab initio calculations. Several minima in the poten tial energy surface were found including both physisorbed and chemisorbed s tates in which one third of the water molecules were dissociated. In the mo re stable of the physisorbed states, the water molecules were not all paral lel to the surface, but some showed hydrogen bonding with surface oxygen io ns. Even in the physisorbed state, the geometry of these surface H-bonded w ater molecules were distorted relative to the bulk. One of the stable chemi sorbed states was the same as that found in earlier work by Giordano [Phys. Rev. Lett. 81, 1271 (1998)]. Two more stable chemisorbed structures were f ound in which strong hydrogen bonds to the hydroxide ions in the water laye r were formed. The existence of different minima appears to be the result o f a subtle interplay between hydrogen bonding between adsorbed species and with the surface oxide ions. Harmonic vibrational frequencies were determin ed for both a chemisorbed and a physisorbed states and spectroscopic featur es which should discriminate between chemisorbed and physisorbed states are identified. (C) 2000 American Institute of Physics. [S0021-9606(00)30932-1 ].