One-electron Green function for the Hubbard model including next nearest neighbor hopping

we evaluate the single-particle spectral function of the repulsive Hubbard model in two dimensions, including next-nearest-neighbor hopping, for diffe rent electronic densities, using the moment approach of Nolting. We propose a form for the band narrowing factor, showing up in the fourth moment, tha t takes into account the effect of antiferromagnetic correlations on the ba nd structure. Our results agree qualitatively with QMC calculations. (C) 19 99 Elsevier Science B.V. All rights reserved.