An LCAO-LDF study of the chemisorption of H2O and H2S on ZnO(0001) and ZnO(10(1)over-bar0)

Local density functional theory coupled to the molecular-cluster approach has been used to study the molecular and dissociative chemisorption of H2O and H2S on the relaxed ZnO(0001) and ZnO(<10(1)over bar 0>) surfaces. The geometrical parameters and vibrational frequencies of the adsorbate have been computed. The agreement with experiment is good. Theoretical outcomes indicate that the basicity of the Lewis-base site available on the (0001) surface (the oxygen ions of the second layer partly exposed at the surface) is negligible, and that both H2O and H2S exist even on relaxed ZnO(0001) only as undissociated molecules. At variance to this, the dissociative chemisorption of H2S on relaxed ZnO(<10(1)over bar 0>) is highly favoured, while as far H2O is concerned, dissociative and molecular chemisorption energies are very close to each other.