Potts models: Density of states and mass gap from Monte Carlo calculations

Monte Carlo simulations are performed for first-order phase-transition models. The three-dimensional three-state Potts model has a weak first-order transition. For this model we calculate the density of states on ${\mathit{L}}^3$ block lattices (L up to size 36) and obtain high-precision estimates for the leading partition-function zeros. The finite-size-scaling analysis of the first zero exhibits the expected convergence of the critical exponent ν toward 1/D for large L; in particular, we find ν=2.955(26) from our two largest lattices. Analysis of our specific-heat ${\mathit{C}}_{\mathit{v}}$ data yields l=0.080 31(26) for the latent heat. Along another line of approach, we calculate the mass gap m=1/ξ (ξ is the correlation length) for cylindrical ${\mathit{L}}^2$ ${\mathit{L}}_{\mathit{z}}$ lattices (L up to 24 and ${\mathit{L}}_{\mathit{z}}$=256). The finite size-scaling analysis of these results is also consistent with the convergence of ν toward 1/D, but that the limiting value is 1/D is not yet conclusively established. Some theoretical arguments favor ν→0 in case of a first-order transition in a cylindrical ${\mathit{L}}^{\mathit{D}\mathrm{-}1}$∞ geometry. Therefore, we also applied our approach to the 2D ten-state Potts model, which is known to have a strong first-order transition. In this case we find unambiguous evidence in favor of 1/D as the limiting value.