SELF-ENERGY OF FERROMAGNETIC NICKEL IN THE GW APPROXIMATION

The one-electron excitation spectra of ferromagnetic nickel have been obtained from a first-principles calculation of the self-energy operator within the so-called GW approximation. The dielectric matrix, needed to form the screened potential W, is computed within the random-phase approximation. The quasiparticle energies are in very good agreement with angle-resolved photoemission data. The bottom of the d band is raised by about 1 eV resulting in band narrowing as observed experimentally and the quasiparticle widths are also in favorable agreement with experiment. The exchange splittings, however, are the same for most cases as those given by the local-density approximation in density-functional theory. The satellite at 6 eV is not reproduced. Instead, we found a significant contribution to the spectral weight from quasiparticle peaks around that energy. We discuss the success and the shortcomings of the GW approximation in the light of our results.