Electronic structure and X-ray absorption spectrum of rutile TiO₂

The electronic band structure of rutile TiO 2 has been calculated using the linear muffin-tin orbital (LMTO) method. The X-ray absorption spectrum has also been obtained from the calculated band structure and self-consistent potential. The dipole as well as the quadrupole contribution to the X-ray absorption spectrum has been calculated. The calculated band structure shows that there is a significant 2p (O)-3d (Ti) mixing in the valence band which, however, becomes weaker in the Ti d-dominated conduction band. The valence band is well separated from the conduction band by a direct energy gap which is almost degenerate with the indirect energy gap. A comparison with experiments suggests that the majority of the observed pre-edge and edge features in the Ti K-edge X-ray absorption spectrum are due to 1s to 4p dipole transitions, a result of the small Ti-Ti (3d-4p) hybridization in the conduction band region. The quadrupole transition contribution is found to be insignificant.