Low-pressure metastable phase of single-bonded polymeric nitrogen from a helical structure motif and first-principles calculations

Recognition of helical structural motifs in the experimentally observed cubic gauche (CG) crystal lattice has led to the discovery of a single-bonded nonlayered nitrogen structure that we have named chaired web (CW). First-principles density functional theory calculations reveal that CW, which was originally identified at high pressures, possesses metastability at ambient conditions as well. The metastability is demonstrated by both high-quality phonon dispersion calculations and finite-temperature first-principles molecular dynamics simulations. In addition, the CW phase is thermodynamically more stable than the CG phase in the ambient pressure regime.