First order phase transitions studied in the dynamical ensemble

Abstract

A knowledge of the density of states Ω(ε) of a many particle system (ε is the energy per particle) contains the complete information about its thermal behaviour. In this paper it will be demonstrated that Ω(ε) 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 temperatureT. The usefulness of the approach will be demonstrated for theq-states Potts model withq=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 forq≧5 and a second order transition forq=4.