Reexamination of the long-range Potts model: a multicanonical approach

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We investigate the critical behavior of the one-dimensional q-state Potts model with long-range (LR) interaction 1/rᵈ⁺σ, using a multicanonical algorithm. The recursion scheme initially proposed by Berg is improved so as to make it suitable for a large class of LR models with unequally spaced energy levels. The choice of an efficient predictor and a reliable convergence criterion is discussed. We obtain transition temperatures in the first-order regime which are in far better agreement with mean-field predictions than in previous Monte Carlo studies. By relying on the location of spinodal points and resorting to scaling arguments, we determine the threshold value σc(q) separating the first- and second-order regimes to two-digit precision within the range 3 ≤ q ≤ 9. We offer convincing numerical evidence supporting σc(q)