Molecular Dynamics Study of the Structure and Properties for CL-20/Graphene Composite

Molecular dynamics was applied to study the famous high-energy density compound ε-CL-20 (hexanitro hexaazaisowurtzitane) crystal and ε-CL-20/graphene composite. Graphene was added into the three separate crystalline surfaces of CL-20 to build the CL-20/graphene composite. The vibrational mode, phonon density of states (DOS), binding energy, initiation bond length and elastic coefficient, isotropic mechanical properties (Young's modulus, bulk modulus, shear modulus, Poisson's ratio, Cauchy pressures and K/G) were studied for CL-20 crystals and CL-20/graphene composite. It turned out that the region of 1450–1750 cm−1 and 600–900 cm−1 corresponded to the main vibrational features of ε-CL-20. The ability of graphene to decrease the DOS of CL-20 at different crystalline surfaces was (100) > (001) ≈ (010). The interaction between an individual crystalline surface of CL-20 and graphene was different, and the binding energy of the three crystalline surfaces was ordered as (100) > (001) > (010). A study on the initiation bond length showed that the probable bond length (Lprob) of N–NO2 increased in different extent and it was related to the sensitivity of the CL-20. By adding a little graphene, the mechanical properties of CL-20 could be efficiently enhanced, and the (100) crystalline surface exhibited better overall mechanical properties than the other crystalline surfaces. These findings have guided further studies on the application of CL-20 and its composite.