Electron–electron correlations and structural, spectral and polarization properties of tetragonal BaTiO 3

Abstract To analyze the role of electron–electron correlation effects in structural (local-geometry), spectral and polarization properties of tetragonal BaTiO 3 we apply DFT + U approach. We demonstrate that the system properties drastically change when the value of the local Coulomb repulsion U crosses the critical value U c ≈ 7 eV. In particular, the correlation effects cause a change of the ratio of the in-plane and inter-plane Ti–O bond lengths, which results in a flip of the order of the Ti d -bands and change of the polarizability of the system. Since the consensus value of U in BaTiO 3 is unknown, we discuss how the obtained results may be revealed in experimental data, especially in the optical response and ultrafast charge dynamics, where effective U is dynamically tuned.