While　polynitrogens　are　proposed　to　be　the　hyper　rocket　fuels,　many　of　their　properties　in　the　solid　states　are　unclear.　Herein,　we　comprehensively　investigated　the　thermodynamic　and　kinetic　stabilities,　polymorphs,　and　rocket　performances　of　platonic　and　cubic　gauche　nitrogens,　i.e.　tetrahedral　N-4,　cubic　N-8,　platonic　dodecahedral　N-20　and　cubic　gauche　nitrogen　(cg-N),　using　the　first-principles　calculations.　The　results　showed　that　the　dissociation　barrier　of　tetrahedral　N-4　in　the　gas　phase　(＞200　kJ　mol(-1))　is　high　enough　to　keep　stable.　It　would　be　a　liquid　monopropellant　under　slight　external　pressure　or　low　temperature.　The　specific　impulse　(I-sp)　of　tetrahedral　N-4　is　comparable　to　that　of　liquid　H-2/O-2,　but　it　provides　a　density　of　1.459　g　cm(-3)　with　the　body　centered　tetragonal　packing.　The　conversion　barrier　of　cubic　N-8　in　the　gas　phase　(similar　to　85　kJ　mol(-1))　is　marginal　for　stability.　It　may　be　a　solid　at　ambient　temperature,　and　its　I-sp　exceeds　that　of　liquid　H-2/O-2.　The　crystal　density　of　cubic　N-8　is　1.964　g　cm(-3)　with　the　rhombohedral　centered　hexagonal　packing.　The　dissociation　barrier　for　stability　of　platonic　N-20　in　the　gas　phase　(similar　to　25　kJ　mol(-1))　is　insufficient,　however　it　possesses　a　lattice　energy　above　100　kJ　mol(-1).　Although　the　I-sp　of　platonic　N-20　is　as　powerful　as　that　of　the　liquid　H-2/O-2,　it　has　a　crystal　density　of　2.132　g　cm(-3)　with　the　face　centered　cubic　packing.　For　surface　relaxation,　cg-N　is　unstable　at　the　ambient　condition　with　a　dissociation　barrier　of　similar　to　17　kJ　mol(-1).　While　the　I-sp　of　cg-N　is　less　than　those　of　platonic　nitrogens,　its　effective　impulse　(I-ef)　is　the　best　due　to　an　extremely　high　density　of　3.401　g　cm(-3).　In　respect　of　the　thermodynamics,　the　enthalpies　per　atom　of　platonic　nitrogens　are　always　higher　than　those　of　cg-N　and　epsilon-N-2　from　0　to　100　GPa.　(C)　2016　Elsevier　B.V.　All　rights　reserved.