EXCITATION SPECTRUM OF ONE-DIMENSIONAL SPIN-1 ANTIFERROMAGNETIC HEISENBERG CHAIN - GREENS-FUNCTION APPROACH

The one-dimensional spin-1 Heisenburg antiferromagnetic chain is studi ed by a Green's function technique. The excitation spectrum is obtaine d. The dispersion of excitations for an infinite isotropic chain is nu merically calculated. At k = 0 we obtain a gap 2 Delta which is equal to 0.826J and at k = pi we obtain Delta = 0.41J, which is in very good agreement with the exact numerical results of White and Huse.