Ab initio total energy calculations of copper nitride: the effect of lattice parameters and Cu content in the electronic properties

We have studied the structural and electronic properties of bulk copper nitride by performing first principles total energy calculations using the full-potential linearized augmented plane wave (FP-LAPW) method. In our study we have considered two types of cells: the ideal cubic anti-ReO₃ structure corresponding to Cu₃N, and a unit cell with an extra Cu atom at the center of the cube. In the first case, our calculated lattice parameter a=3.82 Å is in excellent agreement with the experimental value a=3.807 Å. The structure is semiconductor with a small indirect band-gap. The increasing of the lattice parameter results in larger band-gaps. An addition of an extra Cu atom at the center of the cell results in a slightly larger lattice parameter a=3.88 Å, and the structure becomes fully metallic. Our calculated value is similar to the experimental lattice parameter corresponding to a metallic copper nitride film.