Vibrational properties, phonon spectrum and related thermal parameters of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine: a theoretical study.

The vibrational spectrum, phonon dispersion curve, and phonon density of states (DOS) of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) crystal were obtained by molecular simulation and calculations. As results, it was found that the peaks at low frequency (0-2.5 THz) are comparable with the experimental Terahertz absorption and the molecular vibrational modes are in agreement with previous reports. Thermodynamic properties including Gibbs free energy, enthalpy, and heat capacity as functions of temperature were obtained based on the calculated phonon spectrum. The heat capacity at normal temperature was calculated using linear fitting method, with a result consistent with experiments. Graphical Abstract Phonon spectrum and heat capacity of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine from DFT calculation.