关键词: 磷酸盐晶体, 第一性原理, 密度泛函理论, 电子结构, 光学性质

Abstract: 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(PO₃)₂(X=Zn, Cd, Hg), the three cationic ternary phosphate crystals containing d¹⁰ electron configuration. The band gap width of other three materials Zn(PO₃)₂, Cd(PO₃)₂, and Hg(PO₃)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(PO₃)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(PO₃)₂ are 3.13, 2.76, 3.24, respectively. It can be calculated that the birefringence index of Zn(PO₃)₂ at 1 064 nm is 0.032, the birefringence index of Cd(PO₃)₂ is 0.025, and the birefringence index of Hg(PO₃)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.

Key words: phosphate crystal, first-principle, density functional theory, electronic structure, optical property