TRAPPED-HOLE CENTERS CONTAINING LITHIUM AND SODIUM IN MGO, CAO AND SRO - AN AB-INITIO SUPERCELL STUDY

The Li and Na trapped hole centres in MgO, CaO and SrO are studied wit h the periodic ab initio Hartree-Fock program CRYSTAL by using the sup ercell approach. A 64 atom supercell has been used that, in a prelimin ary investigation on the Li-MgO system, has been shown to be large eno ugh to reduce the defect-defect interaction to negligible values. The metal ion M+ = Li+, Na+ and its first nearest neighbours (six oxygen i ons) have been allowed to relax. In all the cases the hole is localize d on an oxygen ion (O-) and M+ and O- relax in opposite directions. Th e calculated geometry after relaxation and the hyperfine and quadrupol ar coupling constants are in reasonable agreement with data from ENDOR experiments. (C) 1998 Elsevier Science Ltd. All rights reserved.