An excess-electron point defect associated with an oxygen vacancy as observed in paratellurite has been modeled and studied using theab initioRHF-SCF molecular orbital method of the Many ELectron Description (MELD) program package. Open-shell electronic structure calculations for obtaining spin densities were performed on molecular clusters Te2O6H6having paratellurite geometry and terminated by hydrogen-like atoms with optimized nuclear charges and O-H distances. Hyperfine and superhyperfine matrix elements were calculated based on the spin densities of theab initioresults, and the effects of spin delocalization, second-order perturbation magnetic contributions, extended CI calculations, double-zeta quality basis functions and defect-centered basis functions on these parameters were investigated. While specific results in excellent agreement with EPR measurements were obtained and strongly support 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.