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.