Band Lineup and Charge Carrier Separation in Mixed Rutile-Anatase Systems

Calculations by the HSE06 functional for rutile and anatase crystals reproduce the observed width of the valence and conduction bands, as well as of the gap. From the band structures the branching point energies are obtained as reference for both phases, allowing us to deduce a generic band alignment scheme without a specific interface model. The results show that both bands of rutile lie higher than those of anatase, so in mixed systems the holes are accumulated in the former while the electrons in the latter. Consequences for photocatalytic and photoelectrochemical applications are discussed.