Local-density-based electronic structure methods are applied to gamma-
NbN (tetragonal Nb4N3) to compare it to the strong-coupling supercondu
ctor NbN (rocksalt structure) and to the recently proposed Pm3m NbN ph
ase, (NbO structure) which has a similar transition temperature. In ce
rtain respects gamma-NbN is intermediate between the other phases, as
might be expected, but overall the electronic spectrum more closely re
sembles rocksalt NbN. The N ion in gamma-NbN is more highly charged (N
-1) than in the other two phases.