Variations in the structural, electronic and optical properties of N-doped TiO2 with increasing N doping concentration

Based on density functional theory, calculations were performed for geometrically optimized N-doped TiO2 models. The effect of N dopant and its increasing doping concentration on the band structure are elucidated. N doping narrowed the band gap of TiO2 and introduced isolated N 2p states within the band gap. The location of N 2p states within the band gap can be optimized by N doping concentration. All N-doped TiO2 models shifted the absorption edge of TiO2 toward visible light region and increasing N doping concentration improved the visible light absorption. N-doped TiO2 model having reduced band gap without any isolated states will improve the photocatalytic response. Our results provide strong theoretical background for existing experiments.