INTERPOLATING SELF-ENERGY OF THE INFINITE-DIMENSIONAL HUBBARD-MODEL -MODIFYING THE ITERATIVE PERTURBATION-THEORY

We develop an analytical expression for the self-energy of the infinit e-dimensional Hubbard model that is correct in a number of different l imits. The approach represents a generalization of the iterative pertu rbation theory to arbitrary fillings. In the weak-coupling regime pert urbation theory to second order in the interaction U is recovered. The theory is exact in the atomic limit. The high-energy behavior of the self-energy up to order 1/E-2 and thereby the first four moments of th e spectral density are reproduced correctly. Referring to a standard s trong-coupling moment method, we analyze the limit U-->infinity. Diffe rent modifications of the approach are discussed and tested by compari ng with the results of an exact diagonalization study.