  The interactions between holes in the Hubbard model, in the low density,
intermediate to strong coupling limit, are investigated by systematically
improving mean field calculations. The Configuration Interaction basis set is
constructed by applying to local Unrestricted Hartree-Fock configurations all
lattice translations and rotations. It is shown that this technique reproduces,
correctly, the properties of the Heisenberg model, in the limit of large U.
Upon doping, dressed spin polarons in neighboring sites have an increased
kinetic energy and an enhanced hopping rate. Both effects are of the order of
the hopping integral and lead to an effective attraction at intermediate
couplings.
