REFINED EMBEDDED-CLUSTER CALCULATIONS FOR TRAPPED HOLE BIPOLARONS IN BATIO3

Embedded-quantum-cluster calculations are used to investigate the form ation of hole-type bipolarons in BaTiO3. These simulations improve on our recent results because of the exact performance of geometry optimi zations of the embedded quantum cluster. Moreover, ion relaxations and electron correlations have been treated consistently. The modelling o f correlations includes Moller-Plesset perturbation theory to second o rder (MP2) and density functional theory (DFT) beyond the local densit y approximation. Both defect-induced crystal relaxations and electron correlation contributions are necessary in order to stabilize trapped hole bipolarons in BaTiO3.