The authors investigate the utility of traditional many-body perturbation theory in highly correlated d-electron systems taking full account of the underlying one-particle structure. Starting from a zeroth order Greens function based on a self-consistent local-density calculation, they have here computed the dielectric matrix of ferromagnetic nickel within the RPA, thus demonstrating the feasibility of many-body calculations in realistic systems. From the results they obtain the optical absorption, the optical conductivity and the electron-energy-loss spectra. A deviation from experiment in the optical absorption spectrum is easily traced back to the local-density starting point. Using instead quasiparticle energies in the zeroth order Greens function results in much better agreement with experiment. The particle-hole intraction is relatively unimportant in optical absorption and the local-field effects (LFE) are small, especially at lower energies and small momentum transfers. From the dielectric matrix, they also obtain the GW approximation for the electronic self-energy and from there, the quasi-particle bandstructure which compares well with experiment. In particular they obtain the desired band narrowing. On the other hand, they obtain no satellite 6 eV below the Fermi energy and the spin-splitting is too large, thus demonstrating the need for a theory beyond the GW approximation.
 

Physica Scripta Volume T, 46 270-1, 1992.