A DFT + U study on structural, electronic, vibrational and thermodynamic properties of TiO₂ polymorphs and hydrogen titanate: tuning the Hubbard 'U-term'

Structural, electronic, vibrational and thermodynamic properties have been tested when Hubbard parameter U is implemented in density functional theory calculations for TiO₂ polymorphs: anatase, rutile, TiO₂–B and for hydrogen titanate (H₂Ti₃O₇) bulk. Optimum U parameter values were found for each system, balancing geometric changes and electronic properties, namely, U = 4 eV for anatase and TiO₂–B, U = 5 eV for rutile and hydrogen titanate. Although the addition of this parameter improves the prediction of electronic properties, with no significant structural changes, we found that it would not be adequate for predicting vibrational properties. (paper)