Spin correlation function of theS=1antiferromagnetic Heisenberg chain by the large-cluster-decomposition Monte Carlo method

We calculate correlation functions of a one-dimensional spin S=1 antiferromagnetic Heisenberg model by the large-cluster-decomposition Monte Carlo method. We find that the correlation functions are well approximated by modified Bessel functions. This result supports Haldane's conjecture, and the correlation length agrees with that obtained from spin-wave theory using elementary excitation data.