We have performed density functional calculations on the recently discovered energetic molecule, octanitrocubane C-8(NO2)(8). We predict a strongly exothermic dissociation energy and calculate the ionization potentials, electron affinities and vibrational spectra. We predict that the isolated molecule exhibits a symmetry which is higher than that found in the solid. The vibrational density of states shows strong Raman activity at low frequencies and strong IR intensities at high frequencies. We identify a low-energy anharmonic mode which is consistent with the experimentally assumed free torsional rotations of the NO2 groups about their respective C-N axes.