EMBEDDED-CLUSTER AND SUPER-CELL TREATMENT OF CHARGED DEFECTS IN CRYSTALS

Two different approaches are compared for the treatment of local defec ts in crystals, in the framework of the Hartree-Fock approximation: th e super-cell and the perturbed-cluster model. When the defect is charg ed, problems arise whose origin is discussed and for which corrective terms are proposed. The cation vacancy in MgO is considered as a test case. Defect formation energy, relaxation effects, difference electros tatic potential around the vacancy are analyzed for different super-ce ll and embedded-cluster sizes.