高压下LiNbO_3晶体电子结构与光学性质的第一性原理研究

利用基于密度泛函理论的第一性原理超软赝势平面方法研究了外界压强对LiNbO_3晶体态密度,能带结构,电荷密度以及光学性质的影响.能带结构计算表明,价带顶主要由O-2p和Nb-4d态电子贡献,导带底主要由Nb-4d态电子贡献,且带隙随着压强的增加而线性增大.利用复介电函数计算了LiNbO_3晶体在不同压强下光学性质的折射率、反射率、吸收函数,能量损失函数以及光电导率.研究发现:外界压强大于10GPa时,静态折射率保持不变,随外界压强的增加,反射率、吸收函数以及光电导率区间有一定程度的拓宽,损失函数峰发生"蓝移".研究表明,外界高压可以有效调控LiNbO_3晶体的电子结构和光学性质,为LiNbO_3晶体的高压应用提供了有益的理论依据.

First-principles study electronic structures and optical properties of LiNbO3 under high pressure

The effects of the external pressure on the density of states, band structure, charge density and optical properties of lithium niobate are investigated based on the first-principles density functional theory with the plane wave psuedopetential method. It is found that the top of the valence band is mainly determined by the orbital electrons of O-2p and Nb-4d, the band gap presents a linear increased trend with the external pressure increasing. Moreover, the refractive index, the reflectivity, absorption coefficient, the energy loss function and the conductivity of optical properties of the lithium niobate crystal are calculated by the complex dielectric function under different pressures. The result show that when the external pressure is greater than 10Gpa, static refractive index remains constant, variation range of the reflectivity rate, the absorption function and the conductivity rate are widened as the external pressure increases. The peaks of energy loss function exhibit blue shift with the external pressure increasing. Our results show that the electronic structures and optical properties of LiNbO3 can be effectively modulated by changing external high pressure, which provides a useful theoretical basis for the further application of the the lithium niobate crystal under high pressure.