FIRST-ORDER PHASE-TRANSITIONS IN THE CANONICAL AND THE MICROCANONICAL ENSEMBLE

In the canonical ensemble any singularity of a thermodynamic function at a temperature T-c is smeared over a temperature range of order T-c/N. Therefore it is rather difficult to distinguish between a discontinuous and a continuous phase transition on the basis of numerical data obtained for finite systems in the canonical ensemble. It is demonstrated for four model systems that this problem cannot be circumvented by considering higher cumulants of the energy distribution or cumulant ratios. On the other hand, the distinction between first and a second order phase transition is rather direct if based on the microcanonical density of states which is readily obtainable in the dynamical ensemble.