DYNAMICAL PROPERTIES OF ONE-DIMENSIONAL ANTIFERROMAGNETS - A MONTE-CARLO STUDY

A combination of world-line quantum Monte Carlo and maximum-entropy methods is used to calculate the dynamic structure factor S(alphaalpha)(q,omega) for one-dimensional antiferromagnets. A comparison to exact results demonstrates that qualitative features of spectra are reproduced, but are broadened. The broadening is frequency dependent with low-frequency features being reproduced most accurately. Peak positions are well described. Results for the Heisenberg model with S less-than-or-equal-to 2 demonstrate the qualitative difference between the dynamics of half-integer and integer spins predicted by Haldane. From the positions of the low-temperature q = pi peaks quantitative estimates are produced for the S = 1 and 2 gaps. The q = pi peak position for S = 1 increases with temperature in agreement with experiment. When on-site anisotropy is included for S = 1 a gap splitting results that resembles that found for NENP [Ni(C2H8N2)2NO2ClO4].