Theoretical insight into the influence of molecular ratio on the stability, mechanical property, solvent effect and cooperativity effect of HMX/DMI cocrystal explosive

Molecular dynamics method was employed to study the binding energies of the selected crystal planes of the 1,3,5,7-Tetranitro-1,3,5,7-Tetrazacyclooctane (HMX)/1,3-dimethyl-2- imidazolidinone (DMI) cocrystal in different molecular molar ratios. The mechanical properties were estimated in different molar ratios. Solvent effects were evaluated and the cooperativity effects were discussed in the HMX···HF···DMI ternary by using the M06-2x/6-311+G(2df,2p) and MP2(full)/6-311+G(2df,2p) methods. The results indicate that the substituted patterns (020) and (100) own the highest binding energies. The stabilities of cocrystals in the 1:1 and 2:1 ratios are the greatest, and thus the HMX/DMI cocrystals prefer cocrystallizing in the 1:1 and 2:1 molar ratios, which have good mechanical properties. The sensitivity change of cocrystal originates from not only the formation of intermolecular interaction but also the increment of bond dissociation energy of the N-NO2 bond. The cooperativity effect appears in the linear complex while the anti-cooperativity effect is found in the cyclic system. DMI binding to HMX is not energetically and structurally favored in the presence of HF. This is perhaps the reason that the solvent with large dielectric constant weakens the stability of the HMX/DMI cocrystals. Therefore, the solvents with low dielectric constants should be chosen in the preparation of HMX/DMI cocrystals.