Bi_2Se_3、Bi_2Te_3和Sb_2Te_3的声子和热力学性质的第一性原理研究

First-principles calculations of phonon spectrum and thermodynamic properties of Bi_2Se_3、Bi_2Te_3 and Sb_2Te_3

基于第一性原理的密度泛函理论,在未考虑和考虑自旋-轨道耦合(SOC)的情况下分别优化拓扑绝缘体Bi2Se3、Bi2Te3和Sb2Te3的结构,计算它们的声子谱及热力学性质.基于广义梯度交换相关泛函及SOC效应,计算得到三种物质的声子频率比不考虑SOC时更吻合实验数据.最后计算出三种物质的赫尔姆赫兹自由能F,内能E,等体热容CV和熵S随温度的变化趋势.

The structures of Bi2Se3, Bi2Te3 and Sb2Te3were optimized using density-functional theory（DFT） based on first-prin- ciples with and without spin-orbit coupling（SOC） effect. Phonon spectrums and thermodynamic properties of Bi2 Se3 , Bi2Te3 and Sb2Te3 were calculated. The phonon spectrums for the three compounds were performed within the generalized gradient approxi- mation（GGA） including SOC effects. The results showed that the calculated phonon frequencies by means of optimal structures with SOC were in better agreement with experimental data than that without SOC. Finally,the variation of their free energy（ F）, internal energy（ E）, specific heat at constant volume（ Cv ）and entropy（S） with different temperature were calculated.