Abstract: Nitrogen clusters have drawn considerable attention in recent years, because of not only their theoretical interest, but also their possible use as environmentally friendly high-energy-density materials(HEDMs). In this work, quantum chemical ab initio method has been applied to the study of seven cage-like N₁₂ isomers , including two previously studied nitrogen cages N₁₂. Full geometry optimization, harmonic vibrational frequency, and thermodynamics calculations for seven different N₁₂ molecules have been performed at the RHF/6-31G * level of theory. The calculation results show that all of the seven structures were found to be local minima on the potential energy hypersurface at the RHF/6-31G^*, and the cage-like N₁₂ with D_3d symmetry is the most stable in seven N₁₂ isomers. From the results presented here, it seems that there is not a direct relationship between the stability of the isomers and their symmetry. We also found that the five-membered ring is a fundamental stable structural unit for large even number nitrogen clusters. The more the five-membered rings, the more stable the isomer would be. In addition, the energy differences relative to six N₂ molecules are also calculated and it appears that these seven cage-like N₁₂ isomers would be very energetic materials. The present study would provide some theoretical data for synthesizing more stable nitrogen clusters in the future.

Key words: N₁₂ clusters, Ab initio, High energy density material(HEDM)