Modeling stoichiometric and oxygen defective TiO₂ anatase bulk and (101) surface: structural and electronic...

We present a periodic hybrid DFT investigation of the structural and electronic properties of both stoichiometric and oxygen-defective TiO₂ anatase bulk and (101) surface, in singlet and triplet spin states. In all cases, an excellent agreement with available photoelectron spectroscopy data has been obtained, reproducing the offsets of the deep defect levels positions from the conduction band minimum of TiO₂ created upon oxygen vacancy (V_O) formation. For the bulk, different local structural polaronic distortions around the V_O site have been evidenced depending on the spin state considered. Although a similar conclusion has been drawn for the defective surface for the nine different vacancy positions which have been considered, large migration of the twofold coordinated surface O atom has also been evidenced, up to the initial vacancy site in some cases. The very good agreement obtained with available experimental data regarding the offsets from the conduction band minimum of the deep defect levels positions both for the bulk and the (101) surface of TiO₂ anatase is encouraging for the application of the proposed hybrid-based computational strategy to TiO₂ surface-related processes such as TiO₂-based photocatalysis in which oxygen vacancies are known to play a key role.

All calculations have been performed with Crystal17, considering different hybrid functionals with both effective core pseudopotentials and all-electron atom-centered basis sets, as well as additional empirical dispersion effects with the D2 and D3 models.