X(PO_(3))_(2)(X=Zn,Cd,Hg)电子结构与光学性质的第一性原理研究

First-Principles Study on the Electronic Structure and Optical Properties of X(PO_(3))_(2)(X=Zn,Cd,Hg)

晶体材料的微观结构对于宏观性能有着决定性的作用,探究材料电子结构与光学性质之间的关系是合成新型材料研究的基础方向之一。本文基于密度泛函理论的第一性原理,系统地对X(PO_(3))_(2)(X=Zn,Cd,Hg),这三例阳离子含d 10电子构型元素的三元磷酸盐晶体的电子结构与光学性质进行了研究。Zn(PO_(3))_(2)、Cd(PO_(3))_(2)和Hg(PO_(3))_(2)三种材料的带隙宽度依次减小,分别为5.089、4.065和2.942 eV。通过分析禁带附近的能带轨道归属,可知X(PO_(3))_(2)的价带顶部由P原子、O原子以及阳离子的d轨道所占据,而导带底部则主要由P原子、O原子以及阳离子的s、p轨道所占据,此外P和相邻O原子的电荷密度分布图有明显重叠,证明P—O键具有较强的共价性。X(PO_(3))_(2)的静态介电常数分别为3.13、2.76、3.24。计算可知在1064 nm处Zn(PO_(3))_(2)的双折射率为0.032,Cd(PO_(3))_(2)的双折射率为0.025,Hg(PO_(3))_(2)的双折射率为0.024,且通过分别计算化合物以及阴离子基团的双折射大小,分析出材料的双折射是P—O基团和阳离子协同作用的结果。同时对材料进行布居分析,计算元素得失电子的情况,再次验证了P—O基团相对于Zn—O、Cd—O、Hg—O具有较强的共价性。

The microstructure of crystal materials plays a decisive role in macroscopic properties.An important fundamental direction in the synthesis of new materials is to investigate the relationship between electronic structure and optical properties.This study uses the first-principles based on density functional theory to systematically study the electronic structure and optical properties of X(PO_(3))_(2)(X=Zn,Cd,Hg),the three cationic ternary phosphate crystals containing d 10 electron configuration.The band gap width of other three materials Zn(PO_(3))_(2),Cd(PO_(3))_(2),and Hg(PO_(3))_(2)gradually reduces,which are 5.089,4.065 and 2.942 eV,respectively.By analyzing the attribution of the band orbital near the band gap,it can be seen that the top of the valence band of X(PO_(3))_(2)is occupied by P atoms,O atoms and d orbitals of cations,while the bottom of the conduction band is mainly composed of P atoms,O atoms and occupied by the s,and p orbitals of cations.The charge density distribution maps of P and adjacent O atoms overlap significantly,which prove that P—O bonds have strong covalence.The static permittivities of X(PO_(3))_(2)are 3.13,2.76,3.24,respectively.It can be calculated that the birefringence index of Zn(PO_(3))_(2)at 1064 nm is 0.032,the birefringence index of Cd(PO_(3))_(2)is 0.025,and the birefringence index of Hg(PO_(3))_(2)is 0.024.By calculating the birefringence magnitude of the compound and the anion group respectively,it is found that the birefringence is the result of the synergistic action of P—O group and cations.At the same time,the local analysis of the material is carried out,and the loss of electrons of the element is calculated,which further verify that the P—O group has strong covalence compared with Zn—O,Cd—O,and Hg—O.