A systematic search method for finding new high-pressure phases of polymeric nitrogen

A recent discovery of single-bonded polymeric form of nitrogen in diamond anvil cell high pressure experiments [Nature Mat. \textbf{3}, 558 (2004)] opens a new promising direction in the development of high energy density materials. Besides the cubic gauche phase of polynitrogen stabilized in experiment, other yet unidentified metastable phases could emerge under certain experimental conditions. We present a systematic search method for finding metastable phases of single bonded nitrogen based on a set of Peierls distortions of a given reference structure. Using the most basic reference structure, a simple cubic unit cell, our approach not only reproduces all the single-bonded nitrogen phases reported so far, but also reveals many new metastable structures with promising properties. The equations of state of the structures calculated at the first-principles level are studied over a broad range of pressures up to 300 GPa. The stability of the structures is analyzed using directly calculated phonon spectra. This approach can be extended using more complex reference structures and relaxing the constraint of a pure single bonded phase.