New form of polymeric nitrogen from dynamic shock simulation.

For many years there has been significant interest in polymeric phases of nitrogen at low pressure for potential application as an energetic material. This was the result of years of theoretical work indicating potentially meta-stable polymeric nitrogen. Experimental evidence of both an amorphous phase and a cubic-gauche phase has added greatly to this interest [A. F. Goncharov, E. A. Gregoryanz, H. K. Mao, Z. Liu, and R. J. Hemley, Phys. Rev. Lett. 85, 1262 (2000); M. I. Eremets, R. J. Hemley, H. K. Mao, and E. Gregoryanz, Nature (London) 411, 170 (2001)]. While most of the theoretical work has been done on the many crystal phases of nitrogen, little work has been done on simulating amorphous polymeric nitrogen. The original goal of this work was to simulate amorphous polymeric nitrogen at low pressure; however, we unexpectedly found a new form of polymeric nitrogen. Starting from first principles dynamic shock simulation of cubic-gauche nitrogen [W. D. Mattson and R. Balu, Phys. Rev. B 83, 174105 (2011)] we demonstrate a new low pressure porous form that exhibits stability at low temperatures. We describe the detailed procedure of obtaining this structure as well as some of its physical characteristics. Finally, we explore composite structures of this new form of polymeric nitrogen and their possible relationship to an amorphous form.