Covalency and the metal-insulator transition in titanate and vanadate perovskites

A combination of density functional and dynamical mean-field theory is applied to the perovskites SrVO3, LaTiO3, and LaVO3. We show that DFT+ DMFT in conjunction with the standard fully localized-limit (FLL) double-counting predicts that LaTiO3 and LaVO3 are metals even though experimentally they are correlation-driven (Mott) insulators. In addition, the FLL double counting implies a splitting between oxygen p and transition metal d levels, which differs from experiment. Introducing into the theory an ad hoc double counting correction, which reproduces the experimentally measured insulating gap leads also to a p-d splitting consistent with experiment if the on- site interaction U is chosen in a relatively narrow range (similar to 6 +/- 1 eV). The results indicate that these early transition metal oxides will serve as critical test for the formulation of a general ab initio theory of correlated electron metals.