Introducing Nitramide Group into High Energy Density Material Molecule Leads to Enhanced Performance

Although it has been verified by many experimental studies that the design of introducing nitrogen-rich groups into current molecular backbones is a practical method to increase the detonation properties, there is no clear understanding of how energetic explosophores would affect the energy storage density and energy release degree of high energy density materials (HEDMs). The BCHMX (cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]-imidazole) molecule was designed based on the HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) molecule by introducing intramolecular carbon-carbon linkages, which provides an excellent spot to introduce a nitramide group. Thus, we designed the BCHMX-ENO (2,4,6,8,9-pentanitro-2,4,6,8,9-pentaazabicyclo[3.3.1]-nonane) molecule. To examine its properties, we first employed evolutionary algorithms USPEX to predict the crystal structure of BCHMX-ENO. Then, we applied QM-MD (quantum mechanics molecular dynamics) simulations to examine the initial thermal decomposition reactions and used a combination of RxMD (reactive molecular dynamics with ReaxFF force field) and QM-MD simulations to predict the detonation performance of BCHMX and BCHMX-ENO. We found that nitramide group influences initial reaction steps by affecting the molecular spatial distribution, bond length, and atom distance. We predicted that BCHMX-ENO shows improved detonation properties with 7.40% higher Chapman-Jouguet (CJ) pressure, 2.54% higher detonation velocity and 6.60% higher CJ temperature than BCHMX. This is because nitramide group introduction increases HEDM's nitrogen content and oxygen balance, leading to more CO₂, N₂ and fewer carbon clusters at the CJ state. After expansion to normal conditions from the CJ state, fewer CO gases were produced, indicating that BCHMX-ENO is more environmentally friendly than BCHMX. This study uncovers how the specific functional group influences the energetic properties of HEDMs from the atomic perspective, providing useful information for designing environmentally acceptable alternatives with improved properties.