Predicted new structures of polymeric nitrogen under 100–600GPa

•Six new solid nitrogen structures are predicted using USPEX.•P21/m, C2/c, P212121-500, Pnnm, P21 and Cmc21 are proposed for the first time.•Thermodynamic, mechanical and dynamical stabilities are studied at 100–600GPa.•Cmc21 is a metastable phase and other structures are not stable.•Cmc21 structure does not exhibit metallic property at its stable pressure ranges.