  We apply the Green-Kubo (G-K) approach to obtain the thermal conductivity
tensor of $\beta$-1,3,5,7-tetranitro-1,3,5,7-tetrazocane ($\beta$-HMX) as a
function of pressure and temperature from equilibrium molecular dynamics (MD)
simulations. Direct application of the G-K formula exhibits slow convergence of
the integrated thermal conductivity values even for long (120 ns) accumulated
simulation times. To partially mitigate this slow convergence, we apply a
recently implemented numerical procedure [Int. J. Heat Mass Trans. 188, 122647
(2022)] that involves physically justified filtering of the MD-calculated G-K
heat current and fitting the integrated time-dependent thermal conductivity to
a physically motivated double-exponential function. The thermal conductivity
tensor was determined for pressures 1 atm $ \leq P \leq $ 30 GPa and
temperatures 300 K $\leq T \leq$ 900 K. The thermal conductivity
${\kappa}^{\alpha \beta} (T,P)$ increases with increasing pressure, by
approximately an order of magnitude over the interval considered, and decreases
with increasing temperature. The MD predictions are compared to experimental
and other theoretically determined values for the thermal conductivity of
${\beta}$-HMX. A simple, semi-empirical fitting form is proposed that captures
the behavior of $\kappa^{\alpha \alpha} (T,P)$ over the pressure and
temperature intervals studied.
