Molecular Design Of CL-20 Derivatives For High Energy Density Materials

High energy density materials（HEDMs）have received widespread attention for their broad application prospects,including in the fields of military,national defense and aerospace industry.Until now,it has grown to the fourth generation,which is called CL-20（2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane,namely hexanitrohexaazaisowurtzitane）.In our work,we used CL-20 as the basic skeleton,designing series of high nitrogen content derivatives.We hope to select some promising materials by investigating their detonation performances thermal stability and sensitivity systematically based on the density functional theory（DFT）method.The main results are summarized as follows:（1）Six nitrogen-doping CL-20 derivatives were designed and investigated as energetic materials at B3LYP/6-31G**level based on the density functional theory method.Results show that nitrogen-doping derivatives exhibit high crystal densities(1.98～2.18 g cm^-3)and positive heats of formation(451.68～949.68 k J mol^-1).Among nitrogen doping derivatives,2,4,6,8,10,12-hexanitro-2,4,6,8,9,10,12-heptaazaisowurtzitane（A1）,2,4,6,8,10,12-hexanitro-2,3,4,6,8,9,10,12-octaazaisowurtzitane（B1）and 2,4,6,8,10,12-hexanitro-1,2,3,4,6,8,9,10,12-nonaazaisowurtzitane（C1）possess better detonation velocity and pressure than CL-20,and A1 gives the best performance(D_K-J*A1=9.6 km s^-1;P_K-J*A1=43.07 GPa).Moreover,the specific impulse,brisance,and power of N-doping CL-20 derivatives are also higher than that of CL-20.The thermal stability and sensitivity of nitrogen-doping molecules were analyzed via the bond dissociation energy（BDE）,the characteristic height(h₅₀)and electrostatic sensitivity(E_ES).The results indicate that the stability of A1,B1 and 2,4,6,8,10,12-hexanitro-1,2,3,4,6,7,8,9,10,12-decaazaisowurtzitane（D1）is comparable with that of CL-20.Considering detonation performance and stability,A1 and B1 may be promising candidates as energetic materials with superior detonation performance and favorable stability.（2）A new molecule CL-20-NH₂ has been designed by substituting the six hydrogen atoms in CL-20 with six amino-groups（-NH₂）.We optimized the molecule structure and predict to its heat of formation,crystal structure,detonation properties and stability by using DFT method.The results show that the structure of possesses a series of hydrogen bonds,which increases its energy composition and lead to a higher heat of formation and crystal density.Moreover,compared with CL-20,both explosive properties and stability of CL-20-NH₂ have been markedly improved.It is worth mentioning that the value of impact sensitivity(h₅₀)reaches 35.01 cm which is almost improved about three times as large as that of CL-20.Taking all properties into consideration,CL-20-NH₂ is recommended as potential energetic materials which will surpass CL-20.These findings are expected to be helpful for further rational design of novel high-powered HEDMs.