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

Authors
Type
Published Article
Journal
The Journal of Chemical Physics
1089-7690
Publisher
American Institute of Physics
Publication Date
Volume
134
Issue
20
Pages
204509–204509
Identifiers
DOI: 10.1063/1.3587135
PMID: 21639458
Source
Medline

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.

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