Geometries and differential adsorption energies of H, OH, and H
O on a GaN surface. (a) Top view of H, OH, and H2O on a zinc blende GaN(111) surface. (b) Differential adsorption energy of OH (black square) and H (black circle) as a function of surface coverage Θ. The differential adsorption energy of H2O on 0.75 ML of OH-terminated surfaces is also shown by a red square.