Thermal conductivity tensor of β-1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (β-HMX) as a function of pressure and temperature

We have used reverse non-equilibrium molecular dynamics ( RNEMD) simulations to determine the full thermal conductivity tensor for the monoclinic high explosive crystal beta-1,3,5,7-tetranitro-1,3,5,7-tetrazoctane ( beta-HMX). In order to do so for the monoclinic crystal, four directions for heat propagation are used. Effects of the temperature and pressure are investigated between 200 and 500 K and 0 and 5 GPa, respectively, which approximately covers the range where the beta polymorph is stable. Simulations are carried out with the Smith-Bharadwaj non-reactive empirical potential [Smith and Bharadwaj, J. Phys. Chem. B 103, 3570 (1999)], which is known to reproduce well the thermo-elastic properties of HMX. Our results indicate that the thermal conductivity, kappa, is highly anisotropic, with 36% difference between the two extreme values at 300 K and 0 GPa. A simple function is used to interpolate kappa in the pressure-temperature regime considered in this study, which can be used in continuum models. The results from RNEMD simulations compare well with available experimental results from the literature and allow the determination of kappa for any direction and temperature and pressure within or around the fitting interval.

Automated summary

Reverse non-equilibrium molecular dynamics (RNEMD) simulations were used to determine the full thermal conductivity tensor for beta-HMX, a monoclinic high explosive crystal. The results showed a highly anisotropic thermal conductivity with significant variations between different directions, temperatures, and pressures. The simulations compared well with experimental results and provide a useful tool for determining thermal conductivity in different conditions.