高压下BeSe相变和热力学性质第一性原理研究

Ab initio calculation of phase transition and thermodynamic properties of BeSe under high pressure

利用密度泛函理论研究了BeSe的相变、晶格动力学和热力学性质.计算得到的晶格常数、体弹模量以及其对压强的一阶偏导与实验值符合较好.焓的计算结果表明在压强为57.68GPa时BeSe会发生从闪锌矿(ZB)结构到砷化镍(NiAs)结构的相变,与实验值56±5GPa较吻合.BeSe的声子色散曲线计算表明零压下ZB结构满足动力学稳定性,而在高压下ZB结构的动力学稳定性将消失.基于准简谐近似方法,还成功预测了BeSe的热容、热膨胀系数和熵随着压强和温度的变化关系.

The phase transition, lattice dynamical and thermodynamic properties of BeSe have been inves- tigated with the density functional theory. The calculated equilibrium structural parameters agree well with the available experimental and theoretical values. The calculated enthalpies of different structures for BeSe show that the phase transition pressure from the ZB to the NiAs phase BeSe occurs at 57.68 GPa, which is agreement with the experimental data of 56±5 GPa. At zero pressure, the phonon dis- persion curves of ZB phase BeSe do not show any anomaly or instability. Under compression, the pho- non frequencies of ZB phase BeSe are softened to imaginary frequencies, which indicate a structural in- stability. Within the quasiharmonic approximation, the thermodynamic properties including the heat ca- pacity, thermal expansion coefficient and entropy are predicted.