第一性原理研究缺陷对高压下LiF的电子结构和光学性质的影响

基于密度泛函理论下的平面波超软赝势方法,本文计算了102 GPa压力下LiF理想和含空位（Li-1 、F+1）晶体的电子结构和光学性质.结果表明:102 GPa压力下理想LiF晶体有良好的透明性；高压下Li-1及F+1两种空位的存在不影响LiF的光学透明性.分析其原因：LiF是一种带隙很宽的离子晶体,电子发生跃迁需要较高的能量; LiF中F元素的电负性很大，Li的电负性却很小,二者结合的Li-F键键能很高.另外本文还计算了102 GPa压力下理想LiF晶体及Li-1 、F+1两种空位分别存在时的反射、折射率、介电函数和光损失函数等一些光学性质,并将理想和含空位的做了比较，结果表明：102 GPa压力下空位的存在对LiF在可见光范围内这些光学性质都不产生影响，但由于F+1空位的存在使LiF晶体对光的吸收发生了红移现象.

Research on electronic structure and optical properties of LiF with vacancies under high pressure using first principles method

In order to explain the reason of LiF keeping the optical transparency in visible region, the plane- wave ultra soft pseudo method based on the Density-functional theory were used to optimize the ideal crystal structure of LiF under 0 GPa and high pressures with Li-1 and F+1 vacancies .The simulations were performed to calculate the electronic structure and optical properties. The results indicate that the vacancies can not result in absorption band in the visible region of LiF under high pressure. And by analyzing the electronic structure and energy band of LiF, one can find the reasons that LiF keeps transparency in impact compression .The real and imaginary parts of complex dielectric function, the derived optical constants, the absorption coefficient, the refractive index and the reflectivity for the prefect LiF crystal and that with Li-1 and F+1 vacancies under high pressure are calculated and compared. The results show that although vacancies do not influence the optical transparency in visible region, F+1 vacancies can cause the absorption band in the infrared spectrum.