Thermal conductivity of $\beta$HMX from equilibrium molecular dynamics simulations
Abstract
The closely related GreenKubo and Helfand moment approaches are applied to obtain the thermal conductivity tensor of $\beta$1,3,5,7tetranitro1,3,5,7tetrazoctane ($\beta$HMX) at $T=300$ K and $P=1$ atm from equilibrium molecular dynamics (MD) simulations. Direct application of the GreenKubo formula exhibits slow convergence of the integrated thermal conductivity values even for long (120 ns) simulation times. To partially mitigate this slow convergence we developed a numerical procedure that involves filtering of the MDcalculated heat current. The filtering is accomplished by physically justified removal of the heatcurrent component which is given by a linear function of atomic velocities. A doubleexponential function is fitted to the integrated timedependent thermal conductivity, calculated using the filtered current, to obtain the asymptotic values for the thermal conductivity. In the Helfand moment approach the thermal conductivity is obtained from the rates of change of the averaged squared Helfand moments. Both methods are applied to periodic $\beta$HMX supercells of four different sizes and estimates for the thermal conductivity of the infinitely large crystal are obtained using Matthiessen's rule. Both approaches yield similar although not identical thermal conductivity values. These predictions are compared to experimental and other theoretically determined values for the thermal conductivity of $\beta$HMX.
 Publication:

arXiv eprints
 Pub Date:
 October 2021
 arXiv:
 arXiv:2110.08914
 Bibcode:
 2021arXiv211008914P
 Keywords:

 Condensed Matter  Materials Science;
 Condensed Matter  Statistical Mechanics;
 Physics  Computational Physics
 EPrint:
 The following article has been submitted to the Journal of Chemical Physics