Theoretical Studies on the Performance of HMX with Different Energetic Groups

Forty nitramines by incorporating -C=O, -NH₂, -N₃, -NF₂, -NHNO₂, -NHNH₂, -NO₂, -ONO₂, -C(NO₂)₃, and -CH(NO₂)₂ groups based on a 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) framework were designed. Their electronic structures, heats of formation (HOFs), detonation properties, thermal stabilities, electrostatic potential, and thermodynamic properties were systematically investigated by density functional theory. The comprehensive relationships between the structures and performance of different substituents were studied. Results indicate that -C(NO₂)₃ has the greatest effect on improvement of HOFs among the whole substituted groups. Thermodynamic parameters, such as standard molar heat capacity (C _p,m ^θ), standard molar entropy (S _m ^θ), and standard molar enthalpy (H _m ^θ), of all designed compounds increase with the increasing number of energetic groups, and the volumes of energetic groups have a great influence on standard molar enthalpy. Except for -NH₂(R1), -NHNH₂(R5), and B3, all of the designed compounds have higher detonation velocities and pressures than HMX. Among them, E7 exhibits an extraordinarily high detonation performance (D = 10.89 km s^-1, P = 57.3 GPa), E1 exhibits a relatively poor detonation performance (D = 8.93 km s^-1, P = 35.5 GPa), and -NF₂ and -C(NO₂)₃ are the best ones in increasing the density by more or less 12%.