Ab initio study of water adsorption on alpha-Al2O3 (0001) crystal surface

Ab Initio embedded cluster calculations were performed to study water adsor ption on Al-terminated (0001) alpha -Al2O3 surface. We used the surface cha rge representation of the embedding electrostatic potential (SCREEP) model to give an accurate representation of the Madelung potential at the adsorpt ion site. The geometry of the cluster was optimized to take into account th e surface relaxation. Adsorption energies were obtained using the N-layer i ntegrated molecular orbital model (ONIOM). In the case of water adsorption it was found that both dissociative and molecular adsorption minima exist, with adsorption energies of -31.57 and -23.40 kcal/mol, respectively, in ag reement with experiment. Bond orders, covalences and full atomic valences w ere analyzed to investigate the changes in the chemical bonding during adso rption. Our results provide some insight into the scrambling of water and c rystal oxygen atoms during water desorption in isotopic exchange experiment s.