Structure and stability of N7 cluster

Ab initio molecular orbital calculations for seven isomers with low spin of N7 cluster were carried out at the UHF/6-31G*, UMP2/6-31G* and B3LYP/6-31G* levels. Only five of them (structures 1, 2, 4, 7 (Cs) and 7 (C2)) are reasonably local minima on the N7 energy hypersurface. The most stable N7 isomers are the twisted open-chain C2 or Cs structures. In addition to the above seven isomers, two isomers with the spin multiplicity of four were also calculated at the same levels to give an interesting result for structure 6.