New Insights into the Band-Gap Narrowing of (N, P)-Codoped TiO2 from Hybrid Density Functional Theory Calculations

The electronic properties of anatase-TiO2 codoped by N and P at different concentrations have been investigated via generalized Kohn-Sham theory with the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional for exchange-correlation in the context of density functional theory. At high doping concentrations, we find that the high photocatalytic activity of (N, P)-codoped anatase TiO2 vis-a-vis the N-monodoped case can be rationalized by a double-hole-mediated coupling mechanism [Yin et al., Phys. Rev. Lett. 2011, 106, 066801] via the formation of an effective N-P bond. On the other hand, Ti3+ and Ti4+ ions' spin double-exchange results in more substantial gap narrowing for larger separations between N and P atoms. At low doping concentrations, double-hole-coupling is dominant, regardless of the N-P distance.