Hole polarons in pure BaTiO3 studied by computer modeling

Self-trapped hole polarons in technologically important perovskite-type ceramic of BaTiO3 have been modeled by means of the quantum chemical method modified for crystal calculations. The computations are carried out in the self-consistent field (SCF) manner using the embedded molecular cluster model. The spatial configuration of a hole polaron, displacement of defect-surrounding atoms, and wave functions of the polaron ground and excited states are obtained and analyzed. The probability of spontaneous hole self-trapping is estimated in the perfect lattice of the BaTiO3 crystal by calculating the value of the hole self-trapping energy as a difference of the atomic relaxation energy and the hole localization energy. This value is found to be negative, −1.49 eV, which demonstrates the preference of the self-trapped polaron state. The calculated polaron absorption energy, 0.5 eV, is discussed in light of the available experimental data.