Though the Cu 3N crystal is an insulator, it transforms into a semiconductor because of its vacancy doping. (6) Pure Cu 3N has a cubic anti-ReO 3-type structure, where the Cu atom is placed in the center with N 2 atoms at its corners. (1) In recent years, copper nitride (Cu 3N) has gained a lot of interest because of its application as an optical storage device in recorded media, (2−4) in laser writing, (5) and as a battery material because of its unique chemical activity. In modern technology, it plays an important role in integrated circuits and optoelectronic research. The quest for new semiconducting materials is always a driving force in the field of materials science. The experimentally obtained optical band gap and refractive index of the Cu 3N film are 1.44 eV and 2.14, respectively, which are comparable with those from the theoretical approximation. The Cu 3N thin film deposited by the DC magnetron-sputtering technique shows a polycrystalline structure with a nonstoichiometric Cu 3N phase. The density of states exhibits a negligible deformation in Cu–N bonding. The conduction band is dominated by a very small amount of Cu 3p and N 2p orbitals. The band structure of the Cu 3N unit cell shows a strong hybridization of Cu 3d and N 2p orbitals in the near-valence band region ( M) because of their antibonding states which are also observed by molecular orbitals (HOMO–LUMO). The Hubbard ( U) term is added in the local density approximation approach for improvement of the theoretical band gap energy. A comprehensive study on the electronic structure and optical properties of a Cu 3N film is performed by the first-principles study using density functional theory.