N2H: a novel polymeric hydronitrogen as a high energy density material
The polymeric phase of nitrogen connected by lower (than three) order N–N bonds has been long sought for potential application as high energy density materials. Here we report a hitherto unknown polymeric N2H phase discovered in the high-pressure hydronitrogen system by a first-principles structure search method based on a particle swarm optimization algorithm. This polymeric hydronitrogen consists of quasi-one-dimensional infinite armchair-like polymeric N chains, where H atoms bond with two adjacent N located at one side of the armchair edge. It is energetically stable against decomposition above ∼33 GPa, and shows novel metallic feature as the result of pressure-enhanced charge transfer and delocalization of π electrons within the infinite nitrogen chains. The high energy density (∼4.40 kJ g−1), high nitrogen content (96.6%), as well as relatively low stabilization pressure, make it a possible candidate for high energy density applications. It also has lattice dynamical stability down to ambient pressure, allowing for the possibility of kinetic stability with respect to variations of external conditions. Experimental synthesis of this novel phase is called for.