DFT study for combined influence of C-doping and external electric field on electronic structure and optical properties of TiO2 (001) surface

The electron structure and optical properties of C-TiO 2 (001) surface under external electric field were studied by DFT method. After carbon doping, a new impurity level is introduced in the bandgap region of TiO 2 (001) surface, and leads to the decrease of band gap, contributing to the shift of optical absorption to the visible region. When external electric field is applied across the C-TiO 2 (001) surface, the band gap is further reduced with the increase of the electric field intensity from 0.1 eV to 0.5 eV. The electric field over 0.5 eV induces the electronic polarization. The spin-up bands show a gap, while spin-down electrons correspond to a metallic state. The energy gap of spin-up band decreases with increasing the electric field from 0.7 eV to 1.0 eV. The optical absorption of C-TiO 2 (001) shifts to long wavelength compared with pure TiO 2 (001). The electric filed make the optical absorption red-shift further, and the shift increases with an increase of the electric field, especially in the range of 0.7 eV–1.0 eV. The results show that the combined effect of carbon doping and electric field can enhance the photocatalytic activity of TiO 2 (001) surface in visible region.