Optical evidence of 4f-band formation in CeN

We report ab initio calculations of the ground state and optical properties of CeN, which show that the 4f electrons in CeN are itinerant and that the intra-atomic 4f-Coulomb interaction is largely screened. A coherent 4f band of width {~}2 eV is formed, from which an accurate description of the optical spectrum is obtained. The lattice parameter, linear specific heat coefficient, and magnetic susceptibility are also well reproduced. While CeN was previously classified to be a mixed valence compound, our results show that the more appropriate picture is that of a 4f-band material.