关于ErH_2弹性性质及热力学性质的第一性原理研究

First principles study of elastic and thermodynamic properties of ErH_2

利用第一性原理平面波赝势密度泛函理论并结合准谐德拜模型计算了立方萤石结构ErH_2在不同温度和压强下的弹性性质及热力学性质,在高温条件下,计算出的等体热容C_v趋近于Dulong-Petit极限.得到了绝对零度,零压强下立方萤石结构ErH_2的晶格常数为0.5232 nm,与实验值0.5230 nm非常接近;同时,还由不同的原胞体积计算出了该体系的E-V数据;从计算出的高压下的弹性常数,根据立方晶系的力学稳定性条件,推断出立方萤石结构ErH_2的相变压力约为20 GPa,为高压条件下,关于ErH_2结构的进一步实验研究提供了有效的理论参考值.

First principles theoretical study using the plane wave pseudopotential method and the quasiharmonic Debye model is performed for the elastic and thermodynamic properties of ErHz with fluorite structure at different temperatures and pressures. The calculated isochoric heat capacity Cv is convergent to Dulong-Petit limit at high temperature. The calculated lattice parameter of 0. 5232 nm at p= 0 GPa and T=0 K is in excellent agreement with the experimental value of 0. 5230 nm. Simultaneously, the E --V data are also calculated from different unit cell volumes. From the calculated values of the elastic constants at high pressures and the mechanical stability criteria of cubic crystals, the phase transition pressure is found to be about 20 GPa, which is a valid theoretical reference value for further experimental work in high pressure research.