S(q,ω) for the S=1/2 and S=1 one-dimensional Heisenberg antiferromagnet: A quantum Monte Carlo study

The dynamic-spin-correlation function S(q,ω) is computed for the one-dimensional antiferromagnetic Heisenberg model for S=1/2 and S=1. Imaginary-time correlation functions are evaluated with the quantum Monte Carlo method and the maximum-entropy method is used to continue these results to real frequencies. This technique produces a value for the S=1 Haldane gap that agrees with previous work and also gives a good description of inelastic neutron scatter- ing data for the one-dimensional S=1/2 antiferromagnet ${\mathrm{CuCl}}_2$⋅2N(${\mathrm{C}}_5$${\mathrm{D}}_5$).