CONCLUSION

Despite the impressive advances in preparing of co-crystals based on the CL-20 cages, we believe that co-crystallization is not the only way for improving the characteristics of CL-20. In particular, substituted CL-20 derivatives demonstrate some advantages over the pristine CL-20 and other nitroamine high-energy systems. Computer simulation is a cheap and suitable way for the selection of the most stable and powerful compounds among a wide variety of CL-20 derivatives. Efforts to synthesize new CL-20-like cages should be preceded by the comprehensive theoretical studies.
In the presented study, we consider pyrolysis mechanisms, stability, and reactivity of two promising silicon CL-20 derivatives as well as their dimers. We obtain that the presence of silicon atoms in the cage changes the mechanisms of initial pyrolysis step, but does not significantly reduce the stability of the cage. In addition, Si-containing cages are more prone to dimerization. On the other hand, the simultaneous presence of silicon and fluorine atoms results in the compound instability.
With regard to the presented results as well as the previously published data, the CSi5H6N12O12 compound seems to be the most attractive structure. It demonstrates higher crystalline densities, decomposition reaction heats, detonation velocities, detonation pressures, and explosion temperatures than the pristine CL-20.\cite{Tan_2014} At the same time, according to the presented results, its kinetic stability, frontier orbitals, and chemical reactivity is very similar to the CL-20 characteristics. The possibility of CSi5H6N12O12 synthesis from the silicon analogies of benzylamine and glyoxal or other precursors is a rather difficult task, which requires particular consideration.