1ST ORDER PHASE-TRANSITIONS STUDIED IN THE DYNAMIC ENSEMBLE - THE Q-STATES POTTS-MODEL AS A TEST CASE

A knowledge of the density of states OMEGA(epsilon) of a many particle system (epsilon is the energy per particle) contains the complete information about its thermal behaviour. In this paper it will be demonstrated that OMEGA(epsilon) can very efficiently and precisely be determined by a Monte Carlo calculation in an ensemble where the system of interest is coupled to another system of comparable size. This is in contrast to the canonical approach where the system of interest is coupled to an infinite bath at a temperature T The usefulness of the approach will be demonstrated for the q-states Potts model with q=4, 5, and 8 where the numerical data can be compared with exact results. In our numerical data we can clearly identify a first order phase transition for q greater-than-or-equal-to 5 and a second order transition for q=4.