Electronic and optical properties of pure and Mo doped anatase TiO2 using GGA and GGA+U calculations

Comparative GGA and GGA+U calculations for pure and Mo doped anatase TiO2 are performed based on first principle theory, whose results show that GGA+U calculation provide more reliable results as compared to the experimental findings. The direct band gap nature of the anatase TiO2 is confirmed, both by using GGA and GGA+U calculations. Mo doping in anatase TiO2 narrows the band gap of TiO2 by introducing Mo 4d states below the conduction band minimum. Significant reduction of the band gap of anatase TiO2 is found with increasing Mo doping concentration due to the introduction of widely distributed Mo 4d states below the conduction band minimum. The increase in the width of the conduction band with increasing doping concentration shows enhancement in the conductivity which may be helpful in increasing electron-hole pairs separation and consequently decreases the carrier recombination. The Mo doped anatase TiO2 exhibits the n-type characteristic due to the shifting of Fermi level from the top of the valence band to the bottom of the conduction band. Furthermore, a shift in the absorption edge towards visible light region is apparent from the absorption spectrum which will enhance its photocatalytic activity. All the doped models have depicted visible light absorption and the absorption peaks shift towards higher energies in the visible region with increasing doping concentration. Our results describe the way to tailor the band gap of anatase TiO2 by changing Mo doping concentration. The Mo doped anatase TiO2 will be a very useful photocatalyst with enhanced visible light photocatalytic activity.