Postulated in 1992 and synthesized in 2004 above 2000 K and 110 GPa, the singly-bonded nitrogen cubic gauche crystal (cg-PN) is still considered to be the ultimate high energy density material (HEDM). The search however has continued for a method to synthesize cg-PN at more ambient conditions or find HEDMs which can be synthesized at lower pressure and temperature. Here, using ab initio evolutionary crystal prediction techniques, a simpler nitrogen-based molecular crystal consisting of N6 and N2 molecules is revealed to be a more favorable polynitrogen at lower pressures. The energetic gain of 534 meV/atom over cg-PN and 138 meV/atom over the N8 molecular crystal at zero pressure makes the N6–N2 system more appealing. Dynamical and mechanical stabilities are investigated at 5 and 0 GPa, and vibrational frequencies are assessed for its Raman and IR spectra. The prospects of an experimental synthesis of the N6–N2 polymeric system compared to cg-PN is higher because the C2h symmetry of N6 within this crystal would be easier to target from the readily available N3- azides and the observed N3+ and N3∗ radicals.
|Original language||English (US)|
|State||Published - Dec 2022|
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