Besides N2, what is the most stable molecule composed only of nitrogen atoms?

Polynitrogen molecules were examined systematically at high levels of ab initio and density functional theory. Besides N2, the thermodynamically most stable Nn molecules, located with the aid of a newly developed energy increment system, are all based on pentazole units. The geometric, energetic, and magnetic criteria establish pentazole (2) and its anion (3) to be as aromatic as their isoelectronic analogues. The bond lengths in 2 and 3 are equalized.