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

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