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

Abstract

Density functional theory has been used to study lithium intercalation into TiO${}_{2}$(B) at low to moderate concentrations [$0lx(\mathrm{Li})\ensuremath{\le}0.25$] 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 Li${}_{x}$TiO${}_{2}$(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 $x(\mathrm{Li})=0.25$, which challenges the interpretation of previous neutron data that, at this composition, the C site is preferentially occupied.