CALCULATION OF PROPERTIES OF CHARGED DEFECTS IN BAFBR AND SRFCL

Embedded quantum clusters treated by Hartree-Fock methods have been used to model V(K) (molecular halogen anion) and impurity (O2-, O-, and OH-) centers within SrFCl and BaFBr. Different representations involving either fixed-point ions or shell-model ions have been considered as the embedding ions. The results consistently show that the out-of-plane Cl2- or Br2- V(K) center is the most easily formed of the possible V(K) centers. Oxygen ions (O2-) substituted at a halide ion site attract a neighboring halide ion vacancy and form an energetically stable trap for holes. It is found that upon ionization the resulting O- species is displaced along the c axis when substituted for Cl- or Br-, but remains on site when substituted for F-. The different levels of calculation show qualitative similarities in ionization potential and charge distribution of the defects.