A New Allotrope of Nitrogen as High-Energy Density Material

Abstract

A new allotrope of nitrogen in which the atoms are connected to form a novel N6 molecule is predicted to exist at ambient conditions. The N6 molecule is a charge-transfer complex with an open-chain structure containing both single and triple bonds. The charge transfer induces ionic characteristics in the intermolecular interactions and leads to a much higher cohesive energy for the predicted crystal compared to solid N2. The N6 solid is also more stable than a previously reported polymeric solid of nitrogen. Because of the kinetic stability of the molecules and strong intermolecular interactions, the N6 crystal is shown by metadynamics simulations to be dynamically stable around room temperature and to only dissociate to N2 molecules above 700 K. The N6 crystal can likely be synthesized under high-pressure high-temperature conditions, and the considerable metastability may allow for an ambient-pressure recovery of the crystal. Because of the large energy difference between the single and triple bonds, the dissociation of the N6 crystal is expected to release a large amount of energy, placing it among the most efficient energy materials known today.