The search for the stable monatomic forms of solid nitrogen is of great importance in view of its potential application as a high-energy-density material. Based on the results of evolutionary structure searches, we proposed two high-pressure polymeric structures to be stable beyond the stability field of the synthesized cubic gauche structure-the layered Pba2 or Iba2 (188-320 GPa) and the helical tunnel P2 1 2 1 2 1 structure (>320 GPa). We rule out the low-temperature stability of the earlier

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... roposed black phosphorus structure. Stability fields of the newly predicted polymorphs are within the reach of current experimental techniques.