First-principles calculations of optical properties of perfect and defective MgO crystals at high pressure

The optical-absorption and refractive-index properties of MgO crystal without and with doubly charged Mg and O vacancies (VMg−2 and VO+2) up to 100 GPa were calculated using the first-principles method. The obtained data were mainly used to explore origins of the observed optical-transparency loss and behaviors of the refractive-index change for MgO under relatively strong shock compression. Results show that the VO+2-induced heterogeneous absorption within ∼300–700 nm should be a source causing the transparency loss. It is found that the refractive index of perfect MgO at 532 nm increases with shock pressure. The VO+2 leads to a rise in refractive index, and the increment increases with shock pressure. If the vacancy concentration increases with shock pressure, effects of the VO+2 on refractive index are enhanced further.