Ab initio calculations of structural, electronic and vibrational properties of BaTiO3 and SrTiO3 perovskite crystals with oxygen vacancies

The first-principles (ab initio) computations of the structural, electronic, and phonon properties have been per-formed for cubic and low-temperature tetragonal phases of BaTiO3 and SrTiO3 perovskite crystals, both stoichio-metric and non-stoichiometric (with neutral oxygen vacancies). Calculations were performed with the CRYSTAL17 computer code within the linear combination of atomic orbitals approximation, using the B1WC advanced hybrid exchange-correlation functional of the density-functional-theory (DFT) and the periodic supercell approach. Var-ious possible spin states of the defective systems were considered by means of unrestricted (open shell) DFT cal-culations. It was demonstrated that oxygen reduction leads to the appearance of new local vibrational modes as-sociated with oxygen vacancies and new first-order peaks in the Raman spectra, which could be used for defect identification. The calculated Raman spectra for different vacancy positions and spins of the system, as well as other properties of defective crystals, are compared with the relevant experimental data.