Effects of the vacancy point-defect on the refractive index and equation of state (EOS) of LiF at high pressure: A first principles investigation

By the first-principles method, the refractive-index and density of LiF crystal without and with charged Li or F vacancy were calculated within 102 GPa, whose results were used to explore effects of shock-induced vacancy point-defects on its refractive-index and EOS at high pressure. Our data indicate that the calculated refractive-index of a perfect LiF crystal increases more rapidly with increasing pressure than those determined by shock experiments and above ∼50–60 GPa there is also a similar behavior in density–pressure curve. It is found that Li1+ vacancy-induced decreases in refractive-index and density are supposed to be a possible source causing these differences. Our results support that the vacancy-defect concentrations should increase with increasing shock-pressure.