【摘要】 基于密度泛函理论的第一性原理计算，本文首次研究了过渡金属卤代磷酸酯MBiP₂X₆（M=Cu, Ag; X=S, Se）三维晶体和二维晶体的声子色谱和拉曼散射谱。以反铁电晶体AgBiP₂Se₆为例，根据声子谱的计算结果，验证了低温反铁电相是动力学稳定的。结合声子总态密度可以得到：声子谱光学支的低频部分主要来源于阳离子M⁺和Bi³⁺的刚性平移振动，光学支相对高频部分来源于[P₂Se₆]基团的内振动。此外，对MBiP₂X₆的声子振动模进行了归属和识别，分析其拉曼活性模的振动频率对厚度的依赖关系。研究表明：随晶体结构层数的增加，A_1g（或A）模的振动频率稳定在203 cm^-1,E_g （或E）模的振动频率在430 cm^-1附近红移8 cm^-1左右。在低频(≤100 cm^-1)下，刚性拉曼振动模较为显著，这与发生顺电-铁电相变时阳离子M⁺和Bi³⁺的相对平移有着密切的关系。更多还原

【Abstract】 In this paper, the phonon chromatography and raman scattering spectra of three-dimensional and two-dimensional crystals of transition metal halide phosphate MBiP₂X₆（M=Cu, Ag; X=S, Se） have been studied for the first time using first-principles calculations based on the density functional theory. The phonon spectra of AgBiP₂Se₆are calculated. According to the calculated results show that the antiferroelectric phase at low temperature is dynamically stable. Combined with the total density of states of phonons, it can be concluded that the low frequency part of the optical branch of phonon spectrum mainly comes from the rigid translational vibration of cation M⁺ and Bi³⁺, and the relatively high frequency part of the optical branch comes from the internal vibration of [P₂Se₆]. And the Raman spectroscopy of MBiP₂X₆ three-dimensional and two-dimensional crystals obtained identifies and categorizes the vibration modes, and analyzes fluctuation of Raman active vibration frequency with the thickness of layered ferroelectric crystal MBiP₂X₆. The results indicate that the vibration frequency of the A_{1 g}（A） symmetric mode hardly any fluctuation around 203 cm^-1 with the increasing layers while E_g（E） mode presents around a redshift of 8 cm^-1 near 430 cm^-1, respectively. At low frequency(≤100 cm^-1), the rigid Raman mode is more significant, which is closely related to the movement of cations M⁺ and Bi³⁺ during the phase transition of paraelectric-ferroelectric.更多还原