Metastability of atomic phases of nitrogen

The metastability of a recently proposed candidate for a polymeric structure for nitrogen is examined using linear response theory to calculate the phonon dispersion throughout the Brillouin zone. It is found that the structure is mechanically stable at pressures below 360 GPa. In contrast, nitrogen in the simple-cubic structure is found to be unstable over the same pressure range. Calculations of Raman- and infrared-active phonon frequencies are presented for the metastable phase.