A theoretical study of the Na-TiO2 (001) rutile interaction

A theoretical study of the reduction of the TiO2 (001) rutile surface by atomic Na is reported. The study is based on ab initio embedded cluster calculations carried out for two different sites of this surface. The first one (A) is represented by a TiO44- cluster and the second (B), an oxygen ending site, by a cluster of formula TiO68-. The calculations show that adsorption of Na is possible on both sites although site A is energetically favored. The electron transfer process has been examined from state averaged complete active self consistent field (CASSCF) calculations. The analysis of the these wave functions shows that the Na 3s electron is transferred to a Ti 3d orbital of the surface only on site A. For site B such a transfer would involve an excited state of the cluster. The dissociation curves for several electronic states are reported.