Microcanonical analysis of a finite three-dimensional Ising system

All singularities which occur at phase transitions are smeared out in finite size systems. It is the purpose of this paper to show that this smearing is a characteristic of the canonical ensemble. It can be greatly reduced if the microcanonical ensemble is used. In order to demonstrate this the density of states of a three-dimensional 10×10×10 Ising system is determined numerically and is analysed in terms of a model entropy. The critical exponents and turn out to be not too far from the values which have been obtained by critical scaling.Dedicated to Prof. H. Wagner on the occasion of his 60th birthday