Statistical Thermodynamics of Bound States and Phase Transitions in Nonideal Plasmas

Abstract

The two principal methods: Grand canonical and canonical description are introduced and compared with respect to bound states. It is shown that a fugacity expansion (grand ensemble) is well suited to describe bound states of a few particles. Therefore the grand ensemble is the natural representation for bound state systems. However on the other hand, fugacity expansions are not appropriate to describe the effects of short range forces. But already a few terms of a density expansion (canonical ensemble) which is not appropriate for bound states give a good representation of short range interactions. The chemical picture, with is to be interpreted as a mixed representation, is combining the advantages of both descriptions. The stability analysis of the thermodynamic functions shows the existence of additional phase transition at high temperatures and high pressures due to nonideality effects. It is shown that phase transitions are much easier to detect in mixed representations (chemical picture) than in the grand canonical ensemble (fugacity expansions).