Berlin 2008 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 29: Poster II

DY 29.1: Poster

Thursday, February 28, 2008, 16:00–18:00, Poster C

Constant Pressure Ensemble: Application to Small Systems and Relation to Einstein Fuctuation Theory. — •Bernhard Joachim Mokross — Instituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Sao Carlos, SP, Brasil, CEP 13560-970

The constant pressure ensemble is the most appropriate to deal with small systems (as clusters and nuclei) since experiments are usually performed under constant pressure conditions. The conjugate variable of the pressure is the volume wherefrom this ensemble partition function requires the sum over discrete unspecified volumes which may lead to errors, presented by the necessity of a correct volume scale, which increase with decreasing size of the system. In order to represent the partition function as a dimensionless integral Koper and Reiss placed the ensemble on a firm fundamental foundation with the derivation of a proper length scale applicable to isothermal fluctuations of any size in ideal fluids. In this paper, by a careful derivation, it is I shown that their result is not limited to isothermal fluctuations in ideal fluids. It applies as well to non-ideal fluids and describes fluctuations which may evolve under conditions not necessarily isothermal. It applies to small systems as well as to systems in the thermodynamic limit where it has a connection with Einstein fluctuation theory. It is also shown how it may be applied to nucleation processes.