Microcanonical Entropy of the Infinite-State Potts Model

Abstract EN

In this investigation we show that the entropy of the two-dimensional infinite-state Potts model is linear in configurational energy in the thermodynamic limit.

This is a direct consequence of the local convexity of the microcanonical entropy, associated with a finite system undergoing a first-order transition.

For a sufficiently large number of states q, this convexity spans the entire energy range of the model.

In the thermodynamic limit, the convexity becomes insignificant, and the microcanonical entropy (the logarithm of the density of states) tends to a straight line.

In order to demonstrate the behaviour of the convexity, we use the Wang-Landau Monte-Carlo technique to numerically calculate the density of states for a few finite but high values of q.

Finally, we calculate the free energy and discuss the generality of our results.