Theory of the Surface Electronic Structure and Defect States of Rutile by the DV-X α Cluster Calculation

The discrete-variational (DV)-X α calculations are applied to the surface clusters Ti 4 O 16,15 and the bulk cluster Ti 3 O 15,14 of rutile (TiO 2 ) with and without the oxygen vacancy. For the clusters with the defect, an occupied localized state is obtained, whose orbital is mainly composed of the d states of the nearest Ti ions. The defect state energy for the surface cluster agrees with that obtained by UPS and ELS experiments. The change in the state density at the valence band calculated for (Ti 3 O 15,14 ) 18- cluster explains satisfactorily the change in the UPS spectra on the Ar or electron bombardment of the ordered (110) surface.