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

To analyze the role of electron-electron correlation effects in structural (local-geometry), spectral and polarization properties of tetragonal BaTiO we apply DFT + approach. We demonstrate that the system properties drastically change when the value of the local Coulomb repulsion crosses the critical value ≈ 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 -bands and change of the polarizability of the system. Since the consensus value of in BaTiO 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 is dynamically tuned.