CORRELATION LENGTH OF 2D POTTS MODELS - NUMERICAL VS EXACT RESULTS

We report Monte Carlo simulations of 2D q-state Potts models with q = 10, 15, and 20 in the disordered phase and compare numerical results for the correlation length xi(d) at the first-order transition point beta(t) with an analytic formula. To measure the exponential decay of the correlation function over several decades with the desired accuracy we made extensively use of cluster-update techniques and improved estimators. As a byproduct we also obtain the energy moments in the disordered phase in very good agreement with a recent large q expansion at beta(t).