Novel high pressure structures of polymeric nitrogen.

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