A series of [N3X](+) (X = O, S, Se, Te) compounds have been examined with ab initio and density functional theory (DFT) methods. To our knowledge, these compounds, except for [N3O](+), are first reported here. The capped triangle structures are global minima for all singlet [N3X](+) systems. Several decomposition and isomerization pathways for the [N3X](+) species have been investigated. The capped triangle [N3X](+) structures are kinetically unstable, and they will easily dissociate into ground-state NX+ and N-2 molecules. The pyramidal [N3X](+) species are likely to be stable because of their moderate dissociation or isomerization barriers (25.4-45.0 kcal/mol), and they may be regarded as suitable candidates for high energy-density materials (HEDMs) if they can be synthesized. The rhombus [N3S](+) is also likely to be stable, but the rhombus [N3Te](+) is not likely to be stable, and if it is formed in any process, it will transform into the pyramidal structure.