单轴应变下CaO和SrO电子结构和光学性质的第一性原理研究

First-principle study on the electronic structures and optical properties of CaO and SrO under uniaxial strains

为探究不同单轴应变条件时碱土金属氧化物CaO和SrO晶体材料电子结构和光学性质的影响，采用第一性原理计算方法，利用密度泛函近似理论，对晶体的能带结构、态密度和介电函数进行计算，并利用克喇末一克朗尼格关系得出晶体的光学常数．研究结果表明：无应变时，CaO和SrO晶体是宽禁带且具有直接带隙的铯缘体，施加单轴应变使晶体带隙的宽度变窄，导电性能增强，且单轴压应变对晶体电子结构的影响比拉应变对晶体电子结构影响明显．2种晶体均为各向同性材料，单轴拉应变使静介电常数变大，单轴压应变使静介电常数变小．光子能量在0～15ev时，2种材料折射率、吸收系数和反射率等光学谱的峰位和峰值均受单轴应变的影响较大，单轴拉应变使得各光学谱的峰位向能量低的方向移动，峰值升高；单轴压应变使得光学谱的峰位向能量高的方向移动，峰值降低．同时单轴拉应变使晶体静态介电常数和静折射率增大，压应变使之降低．研究表明单轴应变可以有效调节CaO和SrO的电子结构和光争胜质．

In order to investigate the impact of uniaxial strain on the electronic structure and optical properties of alkaline earth metal oxides CaO and SrO, the energy band structure, density of states and the dielectric function of the crystals were calculated using the first-principle calculation and density-functional theory （DFT） method, and the optical constants were obtained based on Kramers-Kroning relations. The calculated results show that CaO and SrO crystals are both wide and di- rect band gap insulators in the case of no strain. The band gaps widths of two materials decrease with both uniaxial tensile and compressive strain, in these two cases their conductivities are enhanced, and the influence of compressive strain on the electronic structure of CaO （SrO） is more obvious than tensile strain. The two crystals are both isotropic materials, the uniaxial tensile strain makes the static dielectric constant larger, and the uniaxial compressive strain makes the static dielec- tric constant smaller. The peaks of positions and values of refractive index of the two material refractive index, absorption coefficient and reflectivity are influenced obviously by uniaxial strain in the energy range from 0 to 15 eV. The uniaxial ten- sile strain makes each optical spectrum peak moving towards the direction of lower energy and the peak value becoming higher, and the uniaxial compressive strain makes optical spectrum peak position moving towards the direction of higher en- ergy and the values of peaks becoming lower. The static dielectric constant and refractive index of two crystals are both in- crease with uniaxial tensile strain and decrease with nniaxial compressive strain. The study shows that uniaxial strain can effectively adjust the electronic structure and optical properties of CaO and SrO.