高压下LaB6的弹性和热力学性质的第一性原理计算

Elastic and thermodynamic properties of LaB6 under pressure: a first-principles study

摘要:

运用平面波赝势密度泛函理论，研究了CsCl结构的LaB6在高压下的弹性和热力学性质. 计算中使用了广义梯度近似，得到在零温零压下LaB6的晶格常数和已知的实验和其它理论结果相符。同时，我们还得到了LaB6的弹性常数Cij，体弹模量B，剪切模量G，杨氏模量E，德拜温度ΘE，泊松系数σ，压缩波速VL和剪切波速VS与压强的关系。计算发现LaB6在低于14 GPa具有力学稳定性. 根据准谐德拜模型，我们还预测了CsCl结构LaB6的热力学性质，对0-14 GPa 和0-1500 K 范围内热膨胀系数和比热容的变化进行了研究. 最后分析了LaB6在零温零压和高压下的电子态密度图.

Abstract:

The elastic and thermodynamic properties of CsCl-type structure LaB6 under high pressure are investigated by first-principles calculations based on plane-wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The calculated lattice parameters of LaB6 under zero pressure and zero temperature are in good agreement with the existing experimental data and other theoretical data. The pressure dependences of the elastic constants, bulk modulus B (GPa), shear modulus G, Young’s modulus E, elastic Debye temperature ΘE, Poisson ratio σ, compressional wave velocity VL and shear wave velocity VS are also presented. An analysis for the calculated elastic constants has been made to reveal the mechanical stability of LaB6 up to 14 GPa. The thermodynamic properties of the CsCl-type structure LaB6 are predicted using the quasi-harmonic Debye model. The variation of thermal expansion coefficient α, the variation of the heat capacity Cv are obtained systematically in the ranges of 0-14 GPa and 0-1500 K. At last, the pressure dependences of the density of states are also investigated.