  In the preprint cond-mat/0701060 we detected a factor two error in the coding
of the Heisenberg term of the Hamiltonian. In the result the exchange term used
in the paper was that of an anisotropic Heisenberg model with $J_x=J_y=J$ and
$J_z=J/2$. Thus all results given for which J=0 was chosen, remain unchanged,
whereas all results containing the exchange parameter remain true for the
extended Hubbard model with anisotropic exchange. That model is of some
interest by itself, due to the relation to the XXZ model. The differing results
for isotropic exchange are given here.
