AB-INITIO MOLECULAR-CLUSTER MODELING OF A PARAMAGNETIC EXCESS-ELECTRON VACANCY CENTER IN PARATELLURITE

An excess-electron point defect associated with an oxygen vacancy as o bserved in paratellurite has been modeled and studied using the ab ini tio RHF-SCF molecular orbital method of the Many Electron Description (MELD) program package. Open-shell electronic structure calculations f or obtaining spin densities were performed on molecular clusters Te2O6 H6 having paratellurite geometry and terminated by hydrogen-like atoms with optimized nuclear charges and O-H distances. Hyperfine and super hyperfine matrix elements were calculated based on the spin densities of the db initio results, and the effects of spin delocalization, seco nd-order perturbation magnetic contributions, extended CI calculations , double-zeta quality basis functions and defect-centered basis functi ons on these parameters were investigated. While specific results in e xcellent agreement with EPR measurements were obtained and strongly su pport the proposed defect model, inability to obtain overall agreement with experiment via a single calculation is suggestive of limitations resulting from cluster size as well as basis set quality and size.