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Computational study of self-trapped hole polarons in tetragonal BaTiO<inf>3</inf>

Abstract:

We have used a quantum-chemical method developed for crystal calculations to investigate self-trapped hole polarons in technologically important BaTiO3 perovskite-type crystal. The tetragonal structure of this material is considered in the present work. The computations are carried out in a self-consistent-field manner using the embedded molecular cluster model. The spatial configuration of a hole polaron and displacements of defect-surrounding atoms are obtained and analyzed. The probability of spontaneous hole self-trapping in a perfect crystal lattice is estimated by calculating 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, -0.87 eV, which demonstrates the preference of the self-trapped polaron state compared to a free hole state in the valence band. The computed polaron absorption energy, 0.4 eV is found to be in an excellent agreement with the available experimental data and independent estimations of the polaron theory.