Theoretical studies on the effects of solvents on the mechanisms of configuration transformation of ε-CL-20

Density functional theory tight binding molecular dynamics (DFTB-MD) and density functional theory (DFT) are used to study the mechanisms of configuration transformation of ε-2,4,6,8,10,12-hexanitro-2,4,6,6,8,10,12-hexaazaisowurtzitane (ε-CL-20) molecule under the effects of toluene and acetone. DFTB-MD results show that a series of configuration transformations occur to ε-CL-20 molecule in ε-CL-20/toluene solution, which is transformed to γ-CL-20 firstly, then to ζ-CL-20, and finally to ω-CL-20, while ε-CL-20 is transformed to α-CL-20, and finally to ω-CL-20 in ε-CL-20/acetone solution. The DFT calculation results indicate that the ε → γ(α) → ζ → ω transformation of ε-CL-20 molecule is thermodynamically feasible. Because γ(α)-CL-20 molecule is thermodynamically the most stable during γ(α)-, ζ-, and ω-CL-20 molecules, only transformation of ε-CL-20 molecule from configuration ε- to γ(α)- has occurred in experiments. Both Bader’s atoms in molecules (AIM) and independent gradient model (IGM) analyses indicate that the C-H···O type hydrogen bond is the main intermolecular interaction in the CL-20/solvent dimer and plays a major role in the formation of the dimer. This work reveals the configuration transformation mechanism of energetic molecules affected by solvent at the micro level, providing theoretical guidance for the preparation of pure form energetic crystals.