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.