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Abstract: We use a two-dimensional Wang–Landau sampling algorithm to map out the phase diagram of a Q-state Potts model with in an external field H that couples to one state. Finite-size scaling analyses show that for large Q the first-order phase transition point at is in fact a triple point at which three first-order phase transition lines meet. One such line is restricted to ; another line has . The third line, which starts at the triple point, ends at a critical point which needs to be located in a two-dimensional parameter space. The critical field is positive and decreases with decreasing Q, which is in qualitative agreement with previous predictions. [Copyright &y& Elsevier]

We study the critical endpoint behavior using an asymmetric Ising model with two- and three-body interactions on a triangular lattice, in the presence of an external field. The simulation method we use is Wang–Landau sampling in a two-dimensional parameter space. We observe a clear divergence of the curvature of the spectator phase boundary and of the magnetization coexistence diameter derivative at the critical endpoint, and the exponents for both divergences agree well with previous theoretical predictions. [Copyright &y& Elsevier]