Optical Response of Charged Oxygen Vacancies in Wide-Bandgap ThO₂ with GW Correction

Experiments suggest that ThO₂ is an optical insulator with a bandgap between 5.0-6.0 eV and the introduction of oxygen vacancy results in an emergence of new optical absorption peak in the visible region of the electromagnetic spectrum. Using a fully ab-initio methodology, we demonstrate how oxygen vacancies effect opto-electronic properties of ThO₂. The bare energies were calculated using density functional theory, whereas G₀W₀ many-body perturbation theory was utilized to extract the excited-state energies. A coupled electron-hole Bethe-Salpeter equation (BSE) was solved with quasi-particle correction from G₀W₀calculation revealing the optical signatures of both pristine ThO₂and ThO₂containing oxygen vacancies at two different concentrations. Our G₀W₀calculations reveal that oxygen vacancy at concentration of 1.6 at% reduces the bandgap from 6.6 eV for pristine ThO₂to 1.06 eV. Consequently, the optical response changes, showing emergence of a new peak at 1.0 eV in the presence of oxygen vacancies, compared to 4.54 eV peak observed in pristine ThO₂ which aligns well with the experimental observations. Furthermore, we investigated the neutral and charged vacancies (+2 charge) within ThO₂ in the G₀W₀+ BSE framework. This comprehensive study of the excited state physics provides valuable insights in to defect physics within ThO₂ and serves as a platform for tuning opto-electronic and transport properties in these materials.