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 surface, based on periodic ab initio Hartree–Fock calculations, is reported. Optimization of the Na atom coordinates shows that the alkali binds the surface through interaction with two protruded and one basal oxygen ions. Upon adsorption 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 the band gap in agreement with the new band observed in the photoelectron spectrum. 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 experiments.