Relevance of Dispersion and the Electronic Spin in the DFT + U Approach for the Description of Pristine and Defective TiO₂ Anatase

A density functional theory + U systematic theoretical study was performed on the geometry, electronic structure, and energies of properties relevant for the chemical reactivity of TiO₂ anatase. The effects of D3(BJ) dispersion correction and the Hubbard U value over the energies corresponding to the TiO₂/Ti₂O₃ reduction reaction, the oxygen vacancy formation, and transition-metal doping were analyzed to attain an accurate and well-balanced description of these properties. It is suggested to fit the Hubbard correction for the metal dopant atom by taking as reference the observed low spin-high spin (HS) energy difference for the metal atom. PBEsol-D3 calculations revealed a distinct electronic ground state for the yttrium-doped TiO₂ anatase surface depending upon the type of doping and interstitial or substitutional defects. Based on the calculations, it was found that a HS state explains the observed ferromagnetism in cobalt-substituted TiO₂ anatase. The results presented herein might be relevant for further catalytic studies on TiO₂ anatase using a large surface model that would be worthwhile for heterogeneous catalysis simulations.