Molecular Dynamics Simulation On The Mechanical Property Of CL–20 And Their Cocrystal

CL–20 is one of the single compound explosives with the highest energy density at present.Due to its high sensibility,it has a very limited usage.Cocrystal technology is a method to get a good explosive structure,which has high energy but low sensitivity.This explosive is much safer than CL–20.In this paper,we mainly employ the molecular dynamics approach to make a theoretical analysis for four types of CL–20 crystal andε–CL–20/TATB cocrystal system.These super-cell models of CL-20,includingα–CL–20,β–CL–20,ε–CL–20 andγ–CL–20,are molecular dynamics simulated by using COMPASS force field,at NPT system and different temperatures（198K,248K,298K,348K and 398K）,then the mechanical property parameters of these crystals are calculated and the lengths of trigger bond also are compared.The result shows that the stiffness and hardness of these CL–20 crystals all go down as the temperature increases.The mechanical property ofα–CL–20 andβ–CL–20 is comparably better than that ofε–CL–20 andγ–CL–20.According to the biggest bond lengths（Lmax）of trigger bonds,N–NO₂,the findings predict the sensitivity order of these four types of CL–20 crystals:α–CL–20>γ–CL–20>β–CL–20>ε–CL–20.This paper adopts polymorph predictor method to predict the structure ofε–CL–20/TATB cocrystal（molar ratio 1:1）and analyzes the mechanical and sensitivity features of cocrystal explosive based on molecular dynamics.It is found thatε–CL–20/TATB cocrystal belongs to P–2₁/c space group and it has high binding energy value.Cocrystal molecules are connected mainly by the strong electrostatic force,Van der Waals’force and hydrogen bond.From the comparison of the biggest bond lengths(L_max)of N–NO₂,it can be learnt that cocrystal can effectively decrease the sensibility of explosive.Thus,the cocrystal is able to lower the stiffness and hardness of explosive but increase its toughness.This paper calculates the mechanical property,the trigger bonds,binding energy and cohesive energy density of three types of crystals with the defects of vacancy,dislocation and doping.The same process also goes to the perfectε–CL–20/TATB cocrystal（010）.By comparing the mechanical performance index,including engineering scale,Cauchy pressure and Poisson’s ratio,it is found that these defective crystals can improve the stiffness and hardness of cocrystal at the normal and slightly low temperature,but dislocation and vacancy can have a complex impact on the mechanical property of cocrystal in the higher temperature.Future comparison of density of the binding energy and cohesive energy shows that the Van der Waals’force in the deficient system has decreased,which suggests that deficiency has influence on the stability of the system.Moreover,by analyzing the biggest bond lengths(L_max)of trigger bonds,it is found that the flaws can increase the sensitivity of cocrystal.