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 (W-Mg(-2) and V-0(+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 V-0(+2)-induced heterogeneous absorption within similar to 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 V-0(+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 V-0(+2) on refractive index are enhanced further. (c) 2012 Elsevier B.V. All rights reserved.