Cutoff dependence of a configuration-interaction approach to the two-dimensional Hubbard model

The two-dimensional Hubbard model near half-filling is studied using a conf iguration-interaction method with kinetic energy cutoffs of 4t, 5t, and 6t. D-wave superconducting order parameter and spin-spin correlation functions are calculated as functions of distance to probe for superconductivity and antiferromagnetism. These calculations do not show indications of d-wave s uperconductivity in the ground state of the two-dimensional repulsive Hubba rd model for the 5t and 6t cutoffs. To understand these results, in particu lar the enhancement of d-wave correlations at a cutoff of 4t, we implement a different cutoff scheme. In this second scheme we introduce a cutoff in t he single particle energies relative to the Fermi surface. Using this secon d scheme, we obtain a significant enhancement for g-wave superconductivity.