Semiempirical computational study of oxygen vacancies in a decahedral anatase nanoparticle

Formation of oxygen vacancies (V_O) is an important step of many catalytic reactions following the Mars van Krevelen mechanism. High rate of oxidation is associated with low energy of V_O formation while high selectivity requires an optimal energy of V_O formation. In the present computational study, enthalpy of V_O formation (ΔH_OVF) is studied in a decahedral anatase nanoparticle (TiO₂)₁₂₁(H₂O)₆ using PM6 method. ΔH_OVF shows large variations for oxygen atoms in different locations on facets, edges and vertices. V_O are much more stable in the (101) facet compared to the (001) facet, while internal V_O are more stable for (101) but equally stable for (001) facet compared to surface vacancies on average. Comparison with literature DFT methods results reveals good consistency and high computational efficiency of the PM6 method for vacancies formation energy. Pm6 also correctly predicts admixture states of the Ti³⁺ within the band gap, but absolute values of electronic band gap and position of admixture states is overestimated and needs scaling factors.