Study on the electronic structures of the reduced anatase TiO2 by the first-principle calculation

Employing the first-principle calculations based on the density functional theory (DFT) and the Molecule Orbital theory (MO), we have researched the electronic structures of the reduced anatase TiO2 and its visible light photoactivity. The study is emphasized on the O vacancy, including the components of the defect states, the relationship with the bulk states and the way in which these electrons occupying the defect states are distributed in the real space. We find that the origin of the visible light photoactivity should be due to the transition of the excited electrons from the defect states σg orbital to the σu orbital in the upper conduction bands, rather than arising from the reduction of the band gap. The calculated results indicate that the localized defect states induced by the neutral and doubly ionized oxygen vacancies are all located in the band gap.

► Complete studies about the O vacancy have been done.
► Model for the origin of visible-light photoactivity is proposed.
► Location of defect states of oxygen vacancies is newly confirmed.