Photoexcitation and Ionization of the Oxygen Vacancy in MgO

Oxygen vacancies are ubiquitous in oxides such as MgO and strongly influence the electronic structure and catalytic and transport properties of these materials. Due to their scientific and technological importance, the electronic excited states of oxygen vacancies in MgO have been studied with a variety of methods both by quantum chemists and solid-state physicists. However, despite considerable theoretical effort over the last decades, a microscopic understanding of absorption and emission processes of single oxygen vacancies in MgO are still under debate. Here, we present a balanced ab initio investigation of the photoexcitation and photoionization process of the oxygen vacancy in MgO. Using a newly developed embedding Bethe-Salpeter equation (eBSE) approach, implemented in the WEST code, we calculate energies and transition matrix elements of all relevant defect excitations. We find absorption and emission energies in good agreement with available experimental results and we provide a detailed understanding of the absorption and emission processes of the neutral and positively charged oxygen vacancy, reconciling different views present in the chemistry and condensed-matter physics community.