摘要
采用基于密度泛函理论的第一性原理平面贋势平面波法对立方相Ca_2Ge的电子结构和声子色散关系进行了研究。分析得到:立方相Ca_2Ge是带隙为0.553eV的直接半导体,导带主要由Ca 3d电子态贡献,决定了立方相Ca_2Ge半导体的特性。由声子色散和声子态密度关系分析得到立方相Ca_2Ge晶格振动声学波由Ca原子和Ge原子贡献,光学波低频段(4.6~5.5THz)主要由Ge原子贡献,高频段(5.5~7.3THz)主要由Ca原子贡献。利用准谐德拜模型研究立方相Ca_2Ge的热力学特性,计算结果表明:恒定温度下,体积变化率、热容和热膨胀系数随压力的升高而降低,体弹模量B随压力的升高而增加;压强恒定条件下,体积变化率和体弹模量B随温度的增加而减小,热膨胀系数和热容随温度的增加而增加,当温度高于800K时,热熔CV受压力的影响较小,且接近Dulong-Petit极限。通过对立方相Ca_2Ge电子结构和热力学特性进行系统的研究得到完整的热力学参量,为Ca_2Ge后期的研究提供理论参考。
The electronic structure and phonon dispersion of cubic Ca2Ge have been systematically studied by the first principles of ultra-soft pseudopotential plane wave methods based on density functional theory.The result shows that the cubic Ca2Ge is a direct bandgap semiconductor with a bandgap of 0.553 eV,the conduction band is mainly formed by Ca 3 d,which determine the characteristics of cubic Ca2Ge.The study of phonon dispersion and phonon density states of cubic Ca2Ge show that Ge atoms in the vibration frequency range of 2-4.5 THz contrib-ute to the acoustic waves,and Ca atoms in 5.5-7.3 THz contribute to the high-frequency optical waves.The thermodynamic properties of cubic Ca2Ge are obtained via the quasi-harmonic Debye model,and it is shown that the volume change rate,heat capacity and expansion coefficient are decreased and the bulk elastic modulus is increased with the increasing stress under the constant temperature.The volume change rate and bulk elastic modulus are decreased and the thermal expansion coefficient and heat capacity are increased with the increasing temperature under the constant pressure.The effect of stress on the heat capacity is little when the temperature rise over 800 K,and the heat capacity is closed to the Dulong-Petit limit.The study of electronic structure,thermodynamic properties and the obtained thermodynamic parameters provide theoretical guidance for the further study of cubic Ca2Ge.
出处
《固体电子学研究与进展》
CAS
CSCD
北大核心
2018年第1期18-24,共7页
Research & Progress of SSE
基金
贵州省教育厅创新群体项目(KY[2016]029)
贵州省教育厅青年人才成长基金(KY[2016]166)
省科技厅科学技术基金(LH[2017]7077and NO.LH[2015]7218)
关键词
Ca2Ge
电子结构
第一性原理
准谐德拜模型
力学性质
Ca2Ge
electronic structure
first-principles
quasi-harmonic Debye model
thermodynamic properties
