ReaxFF reactive dynamics of energetic materials: Coupling mechanical and chemical processes in detonation initiation

We report an approach to large-scale atomistic simulations of chemical initiation processes in shocked energetic materials based on parallel implementation of the ReaxFF reactive force field. Here we present results of reactive molecular dynamics (MD) simulations of shocked Pentaerythritol Tetranitrate (PETN) single crystal, a conventional high explosive. We study a planar wall impact to compare mechanical and chemical response at different speeds. The dominant initiation reactions in both systems lead to the formation of NO2. The lagging secondary reactions lead to a formation of water, nitrogen, and other products. By tracking the position of the shock front as a function of time, we have been able to observe how the shock velocity changes in response to the storage and release of chemical energy behind the shock front. We also investigate the effect of shear along different slip systems on chemical initiation. All calculations are performed with massively parallel MD code GRASP enabling multimillion atom reactive MD simulations of chemical processes in many important stockpile materials.