Ab initio quantum chemical studies of cluster models for doped anatase and rutile TiO2

Cluster models for the anatase and rutile structures of bulk TiO2 were calculated by an ab initio Hartree–Fock method with the purpose of establishing qualitative trends for the size of the band gap upon transition metal doping. Different sizes and stabilization methods of the models (Onsager reaction field method, surrounded by water) were tested. The effect of doping cations on the size of the band gap was studied with the anatase model Ti20M(n+)O42 and the rutile model Ti14M(n+)O30. Doping the anatase model with Ti3+, V3+, Cr3+, Mn3+ and Fe3+ narrowed the anatase band gap and the results were principally in agreement with the photocatalytic activity results of doped anatase. Doping of the rutile model with V3+, Mn3+, and Fe3+ did not have a noticeable effect on the size of the rutile band gap. Chromium(3+), on the contrary, broadened the band gap of the rutile model.