高压下CaF_2结构相变和光学性质的第一性原理计算

利用基于密度泛函理论的第一性原理方法,计算了在压力作用下CaF2的结构相变和光学性质。结果证实了CaF2的压致结构转变的顺序是从氟石结构(空间群Fm3m)转变到PbCl2型结构(空间群Pnma),然后继续转变为Ni2In型结构(空间群P63/mmc)。在Fm3m和Pnma两种结构中,电子带隙随着压力的增加而增加,而在P63/mmc结构中,带隙随着压力的增加开始下降。实验结果显示,直到210 GPa,CaF2没有发生由绝缘体到金属的转变。据此推测,CaF2的金属化压力高于300 GPa。还讨论了压力对CaF2光学性质的影响。

First-Principles Study of Structural Stabilities, Electronic and Optical Properties of CaF2 under High Pressure

An investigation on the structural stabilities and electronic properties of CaF₂ under high pressure was conducted using first-principle calculation based on density functional theory (DFT) with the plane wave basis set as implemented in the CASTEP code. Our results demonstrate that the sequence of the pressure-induced phase transition of CaF₂ is the fluorite structure (Fm3m) to the PbCl₂-type structure (Pnma), and to the Ni₂In-type phase (P6₃/mmc). The energy gap increases with pressure in the Fm3m and Pnma phases, then begins to decrease in the P6₃/mmc phase. The band gap overlap metallization does not occur up to 210 GPa. It is predicted that the metallization pressure of CaF₂ should be over 300 GPa. The pressure effect on the optical properties is discussed.