Quasiparticle band structure for SrTiO3 and BaTiO3: A combined G0W0 and LDA+U approach

We present the quasiparticle band structures of SrTiO₃ and BaTiO₃, two seemingly simple oxides. Previous G⁰W⁰ calculations predicted a band gap around 3.36 to 3.82 eV for SrTiO₃ compared to the experimental value of 3.25 eV. A similar discrepancy between theory and experiment for BaTiO₃ is observed. We show that the fully-converged G⁰W⁰ approach predicts reasonably accurate band gap values for both materials, provided that the calculations are carried out on top of LDA+U solutions. These results emphasize the deficiency of the LDA in describing the localized 3d states, in particular as a mean-field starting point for subsequent many-body perturbation calculations. This work demonstrates the accuracy and applicability of the combined G⁰W⁰ and LDA+U approach in calculating the quasiparticle band structures for materials involving localized 3d states, not only for systems with fully occupied 3d semicore states but also for 3d states which are unoccupied.