Theoretical study of H chemisorption on NiO. II. Surface and second-layer defects

Earlier studies using a cluster model for H chemisorption on an NiO (001) surface have been extended to include an anion vacancy on the surface, an anion vacancy in the second layer, a cation vacancy in the second layer, an aluminum substitution for nickel in the surface, a phosphorous substitution for oxygen in the surface, and a nitrogen substitution for oxygen in the surface. All studies were carried out using self-consistent unrestricted Hartree-Fock techniques. The clusters used to model the solid surface were all embedded in an appropriate point-ion array. It is demonstrated that H is bound to the surface for the cases in which the H approaches atop an anion site that is modified by a nearby vacancy changing the filled shell configuration of ${\mathrm{O}}^{2-}$ to ${\mathrm{O}}^{-}$ or by a substitution for the surface oxygen. A substitutional defect at a nickel site, e.g., aluminum, can also lead to hydrogen bonding.