Low pressure metastable single-bonded solid nitrogen phases

Within the framework of the density functional theory, the possibility of the formation of single-bonded solid atomic nitrogen phases as a result of adiabatic compression of molecular and cluster nitrogen structures at zero temperature has been studied. It has been demonstrated that nitrogen clusters N 8 ( C 2v )-B, which are theoretically predicted as one of the promising candidates for high energy density materials, can transform under compression into a solid atomic phase with crystal lattice symmetry P 2 1 . The P 2 1 phase is dynamically stable under decompression to zero pressure. It is shown that the -N 2 molecular phase transforms under compression into a solid atomic phase with R 3&cmb.macr; c symmetry, and retains a vibrationally stable crystal structure when the pressure is reduced to 30 GPa, transforming into a stable cluster form at lower pressures. The atoms in the P 2 1 and R 3&cmb.macr; c solid atomic phases are linked by single bonds; therefore, these structures can store a large amount of energy 1.4 eV per atom. A detailed comparison of the properties of new P 2 1 and R 3&cmb.macr; c solid atomic phases with other nitrogen crystal structures that are dynamically stable at low pressures has been carried out. New low-pressure high-energy density solid nitrogen phases are theoretically predicted.