A periodic Hartree-Fock study of Na adsorption on the TiO2 (110) rutile surface

A theoretical analysis of the Na adsorption on the TiO2 (110) rutile surfac e, based on periodic ab initio Hartree-Fock calculations, is reported. Opti mization of the Na atom coordinates shows that the alkali binds the surface through interaction with two protruded and one basal oxygen ions. Upon ads orption there is an electron transfer from the 3s Na atomic orbital to the surface, giving rise to a highly spin-polarized state with the spin density localized on the penta-coordinated Ti surface atoms. This state falls in t he band gap in agreement with the new band observed in the photoelectron sp ectrum. The presence of this state induces a shift in the work function of 2.5 eV which is close to the value of 2.6-2.9 eV reported in recent experim ents. (C) 1999 Elsevier Science B.V. All rights reserved.