Theoretical ab initio study of the intrinsic band gap in semiconductor oxides based on modified titanium dioxides

The results of Hartree-Fock calculations mimicking the effect of transition metal ions on electronic and structural properties of rutile and anatase structures have been presented. The vertical excitation energies of modified structures were estimated by performing single point configuration interaction calculations including only singlets (CIS). The main discussion concerns the excitation shifts into a longer wavelengths region and their relation to the frontier orbitals responsible for the observed band gap changes. The results obtained allow us to give some insight into understanding the target phenomenon as well as point out on the importance of boundary frontier orbitals. Particularly, it was shown that the transition metal modified anatase structures prepared by modern ion-engineering techniques are superior compared to those prepared by the use of conventional ones.