THE 2-HOLE GROUND-STATE OF THE HUBBARD-ANDERSON MODEL, APPROXIMATED BY A VARIATIONAL RVB-TYPE WAVE-FUNCTION

In this paper the Hubbard-Anderson model on a square lattice with two holes is studied. The ground state (GS) is approximated by a variation al RVB-type wave function. The holes interact by exchange of a localiz ed spin excitation (SE), which is created or absorbed if a hole moves to a nearest-neighbour site. An SE can move over the sublattice on whi ch it is created. A variational calculation of the GS and the GS-energ y is performed for an open-ended 4 X 4 lattice with two holes with the restriction that the SE is neighbouring both holes and does not move over its sublattice. It is found that the two holes prefer a bound sta te in which their mutual distance is 1 or square-root 2 (with lattice spacing 1).