立方晶系Ca2Si声子色散和热力学性质的第一性原理计算

采用模守恒贋势和超软贋势两种方法分别计算立方晶系Ca2Si的声子色散关系、声子态密度和热力学特性.运用线性响应方法和有限位移方法确定立方晶系Ca2Si的声子色散关系和声子态密度,得到立方晶系Ca2Si的声子振动模式是各向异性,且立方晶系的Ca2Si是不稳定结构.在声子色散关系确定的基础上分别计算定容热容、焓、熵和自由能随温度的变化关系,得到Cv-T曲线在低温条件下符合德拜第三定律;当T=1000K时,立方晶系Ca2Si的热熔Cr=21J·mol-1 ·K-1;在高温条件下,随着温度的增加Cv→3R.通过分析声子色散、振动关系和热力学特性得到立方晶系Ca2Si的振动系统由声子和电子组成.

First-principle Calculation on Phonon Dispersion and Thermodynamic Property of Cubic Ca2 Si

Phonon dispersions,density of phonon states and thermodynamic property of cubic Ca2Si have been calculated by the Norm-Conserving method and Ultra Soft Pseudo-Potential method,respectively.The phonon dispersion and density phonon states of cubic Ca2Si have been confirmed by linear response method and finite displacement method.The result of phonon dispersion and density phonon states show that cubic phase was an unstable structure and the phonon vibration was anisotropic.The heat capacity,enthalpy,entropy and free energy were changed with temperature changing,and the Cv-T curve conformed to the Debye third power law in the low temperature condition.The heat capacity Cv =21 J ·mol-1 · K-1 at 1000 K,in the high temperature condition the CV→3R with the temperature increasing.The results of the study on the dispersion of phonon,phonon density and thermodynamic property were obtained that the oscillatory systems were formed with phonon and electron.