Density of states of a two dimensional XY model from Wang-Landau   algorithm
  Using Wang-landau algorithm combined with analytic method, the density of states of two dimensional XY model on square lattices of sizes $16\times16$, $24\times24$ and $32\times32$ is accurately calculated. Thermodynamic quantities, such as internal energy, free energy, entropy and specific heat are obtained from the resulted density of states by numerical integration. From the entropy curve symptoms of phase transition is observed. A general method of calculation of the density of states of continuous models by simulation combined with analytical method is proposed. 
Jun Xu, H. R. Ma