Electronic structure of GdN, and the influence of exact exchange
  GdN bulk is studied with the local density approximation, on the Hartree-Fock level, and on the level of the hybrid functional B3LYP. A local basis set formalism is used, as implemented in the present CRYSTAL06 release. It is demonstrated that the code is technically capable of treating this system with its 4f electrons explicitly, i.e. out of the core. The band structure at the level of the local density approximation is in good agreement with earlier calculations and is found to be half-metallic. The Hartree-Fock band structure is insulating with a large gap. Interestingly, three solutions were found at the B3LYP level. The lowest of them is insulating for majority spin, and the Fermi surface for minority spin consists only of points, resulting in a very low density of states around the Fermi level. 
K. Doll