Lithium intercalation into TiO₂(B): A comparison of LDA, GGA, and GGA+U density functional calculations

Density functional theory has been used to study lithium intercalation into TiO2(B) at low to moderate concentrations [0<x(Li)≤0.25] with a range of density functionals: LDA, GGA (PW91, PBE, PBEsol), and GGA+U (PBE+U, PBEsol+U), with the GGA+U calculations employing a Hubbard+U correction to the Ti d states. LDA and GGA functionals give the same general behavior, whereas qualitatively different behavior is predicted by GGA+U for electronic structure and the order of stability of occupied intercalation sites. LDA/GGA functionals predict LixTiO2(B) to be metallic, with the excess charge distributed over all the Ti sites. In contrast, GGA+U predicts defect states in the band gap corresponding to charge strongly localized at specific Ti sites. All the considered functionals predict A1 and/or A2 site occupation at x(Li)=0.25, which challenges the interpretation of previous neutron data that, at this composition, the C site is preferentially occupied.