β-HMX 的振动和热力学性质：第一性原理研究。

Vibrational and thermodynamic properties of β-HMX: a first-principles investigation.

机构信息

Collaboratory for Advanced Computing and Simulations, Department of Physics & Astronomy, University of Southern California, Los Angeles, California 90089-0242, USA.

出版信息

J Chem Phys. 2011 May 28;134(20):204509. doi: 10.1063/1.3587135.

DOI:10.1063/1.3587135

PMID:21639458

Abstract

Thermodynamic properties of β-HMX crystal are investigated using the quasi-harmonic approximation and density functional theory within the local density approximation (LDA), generalized gradient approximation (GGA), and GGA + empirical van der Waals (vdW) correction. It is found that GGA well describes the thermal expansion coefficient and heat capacity but fails to produce correct bulk modulus and equilibrium volume. The vdW correction improves the bulk modulus and volume, but worsens the thermal expansion coefficient and heat capacity. In contrast, LDA describes all thermodynamic properties with reasonable accuracy, and overall is a good exchange-correlation functional for β-HMX molecular crystal. The results also demonstrate significant contributions of phonons to the equation of state. The static calculation of equilibrium volume for β-HMX differs from the room-temperature value incorporating lattice vibrations by over 5%. Therefore, for molecular crystals, it is essential to include phonon contributions when calculated equation of state is compared with experimental data at ambient condition.

摘要

采用准谐近似和密度泛函理论，在局域密度近似（LDA）、广义梯度近似（GGA）和 GGA + 经验范德华（vdW）修正下，研究了 β-HMX 晶体的热力学性质。结果表明，GGA 很好地描述了热膨胀系数和热容，但无法产生正确的体弹模量和平衡体积。vdW 修正改善了体弹模量和体积，但恶化了热膨胀系数和热容。相比之下，LDA 以合理的精度描述了所有热力学性质，总体上是 β-HMX 分子晶体的良好交换关联泛函。结果还表明，声子对状态方程有显著贡献。β-HMX 的平衡体积的静态计算与包含晶格振动的室温值相差超过 5%。因此，对于分子晶体，在将计算的状态方程与环境条件下的实验数据进行比较时，必须包含声子的贡献。