DFT Description on Electronic Structure and Optical Absorption Properties of Anionic S-Doped Anatase TiO₂

Plane-wave-based pseudopotential density functional theory (DFT) calculations are used to characterize the doping effect of S substituting for O in anatase TiO(2). Through band structure calculation, a direct band gap is predicted in TiO(2)(-)(x)S(x). Electronic structure analysis shows that the doping S could substantially lower the band gap of TiO(2) by the presence of an impurity state of S 3p on the upper edge of the valence band. Excitations from the impurity state of S 3p to the conduction band may be responsible for the red shift of the absorption edge observed in the S-doped TiO(2). The band gap lowering and red shift of the absorption edge are found to increase as the sulfur concentration increases.