Density functional theory studies on N 4 and N 8 species: Focusing on various structures and excellent energetic properties.

All-nitrogen materials, as a unique branch of energetic materials, have gained huge attentions, of which cyclo-N ₅ ^- derivatives are the representative synthetically reported materials. However, the energetic performance of cyclo-N ₅ ^- compounds has certain limitations and cannot go beyond that of CL-20. In order to reach the higher energy, in this work, we presented two kinds of polynitrogen species, N ₄ and N ₈ . Two isomers of N ₄ and four isomers of N ₈ were fully calculated by using density functional theory (DFT). Theoretical results show that all these polynitrogen materials exhibit excellent heats of formation (7.92-16.60 kJ g ^-1 ), desirable detonation performance (D: 9766-11620 m s ^-1 ; p : 36.8-61.1 GPa), as well as the remarkable specific impulses (330.1-436.2 s), which are much superior to CL-20. Among them, N ₄ -2 (tetraazahedrane) (D: 10037 m s ^-1 ; p : 40.1 GPa; I _sp : 409.7 s) and cube N ₈ -4 (D: 11620 m s ^-1 ; p : 61.1 GPa; I _sp : 436.2 s) have the highest energetic properties, which are expected to become promising high-energy-density-materials. Moreover, electrostatic surface potentials, Frontier molecular orbitals, infrared spectra, natural bond orbital charges, and weak interactions were also investigated to further understand their relationship between structure and performance.
Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
(Copyright © 2022 Lang, Lin, Wang, Xu and Lu.)