Hole polarons in pure BaTiO3 studied by computer modeling

Self-trapped hole polarons in technologically important perovskite-type cer amic of BaTiO3 have been modeled by means of the quantum chemical method mo dified for crystal calculations. The computations are carried out in the se lf-consistent field (SCF) manner using the embedded molecular cluster model . The spatial configuration of a hole polaron, displacement of defect-surro unding atoms, and wave functions of the polaron ground and excited states a re obtained and analyzed. The probability of spontaneous hole self-trapping is estimated in the perfect lattice of the BaTiO3 crystal by calculating t he value of the hole self-trapping energy as a difference of the atomic rel axation energy and the hole localization energy. This value is found to be negative, -1.49 eV, which demonstrates the preference of the self-trapped p olaron state. The calculated polaron absorption energy, 0.5 eV, is discusse d in light of the available experimental data. (C) 2000 John Wiley & Sons, Inc.