Comparison of hybrid density functional, Hartree-Fock, and GW calculations on NiO

The electronic band structure of NiO in the ferromagnetic state is calculated using the B3LYP hybrid density functional, the Hartree-Fock (HF) method, and the GW approximation (GWA) with dielectric functions constructed using either B3LYP or HF wave functions and energy eigenvalues. The band structure from the GWA calculation based on B3LYP wave functions is quite similar to the parent B3LYP band structure; the main differences are in valence bandwidth and in the upward shift of the empty minority spin Ni 3d bands relative to the same bands in the B3LYP calculation. The band structure from the GWA calculation based on HF wave functions differs in that there are large upward shifts in valence band positions in the GWA calculation relative to the HF calculation, which result from screening of the bare exchange term in the Fock operator. Matrix elements of the HF exchange operator are obtained using wave functions from self-consistent HF or B3LYP calculations. Magnitudes of these matrix elements for several states at the Gamma point of the Brillouin zone are compared, and it is found that the only major difference occurs in the empty minority spin bands derived from Ni 3d states of e symmetry. (c) 2006 Wiley Periodicals, Inc.