LOCAL APPROACH TO ELECTRON CORRELATIONS IN FERROMAGNETIC NICKEL

A many-body theory is developed for a multiorbital tight-binding model including intra-atomic interactions. There by, local three-body correlations are taken into account. The theory is applied to the 3d states of ferromagnetic nickel. The multiplet structures of three-particle states are fully taken into account. Their inclusion leads to some states close to the bottom of the 3d bands, thereby strongly influencing the quasiparticle states. The self-energy correction is found to narrow the bandwidth and the exchange splitting as compared with their mean-field values, in good agreement with photoemission experiments. Satellite peaks are found in the spectral function around 6 eV below the Fermi level. Their shapes are quite different for the majority- and minority-spin parts, a feature which has been pointed out before, in particular in connection with finite cluster calculations.