Compressive Shear Reactive Molecular Dynamics Studies Indicating That Cocrystals of TNT/CL-20 Decrease Sensitivity

To gain an atomistic-level understanding of how compounding the TNT and CL-20 energetic materials into a TNT/CL-20 cocrystal might affect the sensitivity, we carried out the compressiveshear reactive molecular dynamics (CS-RMD) simulations. Comparing with the pure crystal of CL-20, we find that the cocrystal is much less sensitive. We find that the molecular origin of the energy barrier for anisotropic shear results from steric hindrance toward shearing of adjacent slip planes during shear deformation, which is decreased for the cocrystal. To compare the sensitivity for different crystals, we chose the shear slip system with lowest energy barrier as the most plausible one under external stresses for each crystal. Then we used the temperature rise and molecule decomposition as effective measures to distinguish sensitivities. Considering the criterion as number NO2 fragments produced, we find that the cocrystal has lower shear-induced initiation sensitivity by 70% under atmospheric pressure and 46% under high pressure (similar to 5 GPa) than CL-20. Based on the temperature increase rate, the cocrystal has initiation sensitivity lower by 22% under high pressure (similar to 5 GPa) than CL-20. These results are consistent with available experimental results, further validating the CS-RD model for distinguishing between sensitive and insensitive materials rapidly (within a few picoseconds of MD).