Reduced Reaction Chemistry Models for TATB and CL-20

Reactive Molecular Dynamics (RMD) simulations with the ReaxFF-lg force field are used to simulate the cook-off chemistry of CL-20 and TATB at a variety of fixed density and fixed temperature conditions. The chemical transformations are monitored using a Coordination Geometry Analysis (CGA) approach which tracks the number and types of bonds associated with each atom. Correlations between these chemical transformations are identified using a Non-negative Matrix Factorization (NMF) approach. These identify reduced chemistry models for these systems containing 6-7 steps. The time histories of these transformations show exponential growth/decay properties that could be fit with Arrhenius rates. From those fits, both activation energies (E_a) and activation volumes (V_a) can be extracted to explain the temperature and pressure dependence of the reactions. Equation of States for the intermediates and products in gamma-law forms can also be derived from the simulations. Both materials show separate low and high-density pathways that can be associated with initial reaction pathways that are dissociative and associative, respectively. This behavior is similar to what has been previously been observed for HMX and RDX, and the reaction rates reflect the observed sensitivities of the materials.