On the choice of exchange–correlation functional for the correct band gap calculation in titanium oxide photocatalysts

In this work the band gap for a set of titanium oxide photocatalysts: TiO2 (rutile, brookite, anatase), SrTiO3, BaTiO3, CaTiO3, MgTiO3, KLaTiO4, K2La2Ti3O10, was theoretically investigated within density functional theory. For the PBE-based hybrid functional the band gap as a function of the fraction of the Hartree-Fock exchange energy (α) was calculated. A correlation between the Goldschmidt tolerance factor and the value of α parameter, that provides an agreement with the experimental band gap, was determined. A wide range of standard hybrid functionals was tested. It was found that the B1WC and WC1LYP hybrid functionals (with α = 0.16) provide the best agreement with experimental data for the set of studied compounds. However, for a more accurate description of the band structure of titanium oxide photocatalysts the α parameter should be chosen accounting for the structural distortion of TiO6 octahedra and their mutual arrangement. The results obtained can be used in predicting the properties of modified structures based on titanium oxides.