MD Simulation Study On RDX And CL-20Crystal And Their Cocrystal And Composite System

In this thesis, molecular dynamics (MD) simulation was applied to investigate ε-CL-20, TNT crystals and CL-20/TNT cocrystal as well RDX/TNT composite. These systems were simulated in COMPASS force field with NPT ensemble at different temperatures.The (2×3×3) and the model cutting along (001) crystalline surface for ε-CL-20crystal primary cells were simulated at five(195K、245K、295K、345K and395K)temperatures. The maximum trigger bond (N-NO2) length (Lmax), the interaction energy (EN-N) between two N atoms in the trigger bond and cohesive energy density (CED) were correlated with sensitivity. These results agree with the experimental fact that the crystal becomes more sensitive as the temperature increases;at the meantime, mechanical properties at different remperatures were abtained and analyzed. For comparison, CL-20/TNT cocrystal and TNT crystal were simulated, the maximum trigger bond (N-NO2) length (Lmax)、cohesive energy density (CED)、 the binding energy(Ebind) and mechanical properties were abtained as increasing temperature and compared with ε-CL-20and TNT crystal. In cocrystal, the maximum trigger bond (N-NO2) length (Lmax) of CL-20was used to correlate with cocrystal sensitivity, and the results showed that cocrystallization can reduce the sensitivity of high energetic explosive. By analyzing pair correlation function g(r) between CL-20and TNT molecular, it is found that hydrogen bond is existing and comes from H atoms of TNT with O atoms of CL-20and H atoms of CL-20with O atoms of TNT. Mechanical properties obtained by fluctuation method show that the values of tensile (E)、bulk(K) and shear(G) modulus fall in between the values of those for ε-CL-20and TNT crystal. However, Cauchy pressure (C12-C44) and K/G for the cocrystal are much larger than those for the other two crystals, which means that malleability is improved. And the model cutting along (100)、(010)、(001) and (120)crystalline surface for the cocrystal were simulated and studied. The models for the composite RDX/TNT with mass ratio2:8,3:7,4:6,5:5and6:4were built and simulated. The Ebind、CED and mechanical properties were abtained, and it is found by correlating its explosive properties that TNT can reduce sensitivity of RDX.