Among homonuclear nitrogen molecules, Ng isomers occupy a critical position as a possible diazide or a benzene analogue. However, the character of stationary points on the N-6 potential-energy hypersurface is known to be a strong function of choice of calculation methods and basis set. We present results with density functional theory (B3LYP and PW91 functionals) and coupled cluster theory (CCSD(T)) to investigate the shape of the potential-energy surface. The CCSD(T) suggests fewer minima on the potential-energy surface compared with the density functional theory. The stability and amount of internally stored energy of Nd isomers as well as their spectroscopic characteristics are important. Structure, vibrational frequencies including IR and CCSD Raman intensities, heats of formation, vertical ionization potentials, electron affinities, and excitation energies are reported.