ON THE USE OF THE QUASI-GAUSSIAN ENTROPY THEORY IN NONCANONICAL ENSEMBLES - II - PREDICTION OF DENSITY-DEPENDENCE OF THERMODYNAMIC PROPERTIES

In previous articles we derived and tested the quasi-Gaussian entropy theory, a description of the excess free energy in terms of the potent ial or full internal energy or enthalpy probability distribution, inst ead of the (configurational) partition function. We obtained in this w ay the temperature dependence of thermodynamic functions in the NVT, N pT and mu VT ensembles assuming a Gaussian, Gamma or Inverse Gaussian distribution. In this article we extend the theory to describe the den sity dependence of thermodynamic properties, using the distribution of volume and number of particles in the isothermal-isobaric and grand c anonical ensemble, respectively. In both ensembles pressure-density ex pressions for a Gaussian and various Gamma distributions are derived a nd applied to water. A Gamma description for the volume distribution t urns out to be a good model in the gas range, which is in accordance w ith the volume distribution of an ideal gas. A Gamma description for t he particle number distribution works well for liquid densities. (C) 1 998 American Institute of Physics. [S0021-9606(98)50332-7].