EMBEDDED-CLUSTER CALCULATIONS FOR TRANSITION-METAL IMPURITIES IN BATIO3

The embedded-cluster technique is used to simulate the local electroni c structure of transition-metal impurities in BaTiO3. The description of the central defect cluster employs an ab initio SCF-MO approach. Th e quantum cluster consists of 21 ions. Outer crystal regions are model led on the basis of a shell-model representation. In all cases defect- induced lattice relaxations have been consistently included. Our resul ts, demonstrated for Mn-Ti(4+), concern optical transitions, Jahn-Tell er effects and questions related to the stability of this defect. The computational level of our ab initio calculations corresponds to Hartr ee-Fock theory (HF) and the configuration interaction (CI). Additional ly, Moller-Plesset perturbation theory and density functional theory h ave been applied to investigate charge-transfer transitions.