In this work, the electronic structures, charge density differenceand optical properties of Si and C codoped anatase TiO2 are studied by using the plane-wave ultrasoft pseudopotential method of density functional theory (DFT). The calculated results reveal that C-Si-codoped anatase TiO2 results in band gap narrowing that increases the probability of electronic transition from the impurity energy levels to the conduction band (about 1.7eV), then improves the solar energy utilization, the existence of impurity energy levels in the forbidden gap reduces the carrier transition energy. The C-Si-codoped TiO2 has been helpful for enhancing the absorption coefficient under visible-light region, especially, among the three models, the third model exhibits the largest value of absorption coefficient under visible-light region.
