Molecular Simulation of the Stability and Thermal Behavior of the Cocrystal CL-20/HMX using LAMMPS and the Force Field ReaxFF

Energetic cocrystals combine properties of multiple materials and can therefore increase the performance of energetic materials. In order to assess new cocrystal compounds, their stability and thermal behavior need to be evaluated. Crucial processes at high temperature are difficult to observe with experimental methods due to the fast reaction time and the high energy output. Molecular dynamic simulations with reactive force fields allow to gain deeper insights into processes as thermal decomposition with atomic spatial and femtosecond-scale time resolution. In contrast "classical" molecular dynamics, the reactive force field ReaxFF allows to simulate the (thermal) decomposition of molecules and arising chemical reactions. With these methods we developed a simulation procedure to evaluate the thermal stability of cocrystals to support finding suitable additives for new cocrystal systems. The procedure was evaluated with the energetic materials CL-20 and HMX, and their cocrystal compound CL-20/HMX. We observed a stabilizing effect of HMX on CL-20 in the cocrystal.