A molecular cluster model of the V o. center in paratellurite

Abstract

A RHF-SCF electronic structure calculation has been performed by means of the MELD program package for a cluster model of the V o .-center, a basic radiation-induced defect in paratellurite identified recently by ESR as an oxygen vacancy defect with a net positive charge. A “perfect” Te 2O 7H 6 cluster has been constructed with an effective core potential and an STO-3G valence basis set complemented by a single Gaussian d-function on Te. The charge distribution inside this cluster has been optimized by adjusting positions and nuclear charges of the peripheral “hydrogens”. A Mulliken analysis of a Te 2O 6H 6 defect cluster derived from the perfect one by removing an O − ion and relaxing both Te's showed that the unpaired spin is primarily concentrated on the Te nearest to the oxygen vacancy with appreciable spin densities on nearby atoms and a substantially modified distribution of the surplus charge. The open-shell wave function has also been employed to derive hyperfine constants, taking into account relativistic corrections in independently calculated values of |; ψ 5 s(0) | 2 and 〈 r −3〉 5 p for the Te atom, but neglecting core polarization. The calculated spin populations and hyperfine parameters account for all major features of the ESR spectra.