Density Functional Theory (DFT) Study on the Structures and Energetic Properties of Isomers of Tetranitro-bis-1,2,4-triazoles

A series of isomers of tetranitro-bis-1,2,4-triazoles were designed, and their electronic structures, heats of formation, densities, detonation performances, thermal stabilities, and impact sensitivities were investigated by density functional theory (DFT). The structure and energetic properties of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) were also calculated at the same level. On comparing with the detonation velocity and pressure and bond dissociation energy (BDE) of HMX, it was found that four isomers (BT2, BT5, BT6, BT7) have higher detonation performances than HMX and three isomers (BT5, BT6, BT7) have better thermal stabilities than HMX. The calculated results of impact sensitivities indicated that all of the designed isomers have more sensitivity than HMX. The calculated results of energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) indicated that all of the designed isomers were more easily excited than HMX in the chemical reaction process. In particular, 3,3',5,5'-tetranitro-1,1'-bis-1,2,4-triazoles (BT5) exhibited excellent detonation performances (9464 m s^-1, 39.44 GPa) and good thermal stability (BDE 256.81 kJ mol^-1). The results indicated that the isomerization of tetranitro-bis-1,2,4-triazoles could improve their detonation performance or thermal stability and might lead to a promising isomer possessing both good performance and high thermal stability.