Molecular Dynamics Simulations of an Initial Chemical Reaction Mechanism of Shocked CL-20 Crystals Containing Nanovoids

To understand the initial chemical reaction mechanism of the heterogeneous explosive hexanitrohexaazaisowurtzitane (CL-20), it is necessary to study the shock initiation mechanism of this nanovoid-containing crystal. In this paper, supercells of CL-20 with different void sizes were constructed. The chemical reactions induced by different impact velocities were calculated using molecular dynamics based on the ReaxFF-lg reactive force field. The effects of impact velocities and void sizes on the chemical reactions of the CL-20 crystal were discussed. The initial reaction of CL-20 molecules around the voids was analyzed, and the evolution of the formation and breakage of chemical bonds as well as the elementary reactions were also obtained. It is found that under an impact, the CL-20 molecules around the voids first undergo polymerization of the N-O bonds and then breakage of the C-N, N-N, and C-H bonds occurs. Increased void size and impact velocity lead to higher temperature "hot spots" and more intense chemical reactions, but have little effect on the breaking sequence of chemical bonds in the CL-20 molecules.