  We present a detailed first-principles DFT study of the equation of state
(EOS), energy-optimized geometries, phase stabilities and electronic properties
of bulk crystalline Cu3N, CuN and CuN2 in a set of twenty different structural
phases. We analyzed different structural preferences for these three
stoichiometries and determined their equilibrium structural parameters.
Band-structure and density of states of the relatively most stable phases were
carefully investigated. Further, we carried out GW0 calculations within the
random-phase approximation (RPA) to the dielectric tensor to investigate the
optical spectra of the experimentally synthesized phase Cu3N(D0_9). Obtained
results are compared with experiment and with previous calculations.
