HALDANE-GAP IN A S=1 EXCHANGE MODEL WITH LONG-RANGE INTERACTIONS

The ground-state properties of the S = 1 Haldane-Shastry model are stu died using a modified Lanczos algorithm and diagonalizing exactly smal l chains. We find evidence that, as for the antiferromagnetic Heisenbe rg model, the spectrum shows a gap, in contrast to the S = 1/2 case. T he correlation functions < S-z(O)S-z(m) > decay exponentially for larg e m. We find that the correlation functions for the Haldane-Shastry mo del decay faster than for the Heisenberg model. We estimate the infini te system limit for the ground-state energy, value of the gap and corr elation functions.