Maria Koulis

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


This research is involved with the construction of potential energy models for the interaction of closed shell atoms and/or molecules and with the study of the thermodynamic properties of pure liquids and liquid mixtures, through the use of statistical mechanical perturbation theory.;The previously developed Exchange-Coulomb potential energy model for the interaction of closed shell atoms is modified to correct its unphysical behaviour for small interspecies distances and so that it is applicable for interactions involving molecules. The new potential energy model is based on using the Heitler-London energy to represent the repulsive part, and a damped and overall corrected dispersion energy series to represent the attractive part, of the interaction energy. It is tested using reliable literature potentials for the Ne-Ne, Ne-Ar, Ar-Ar, N{dollar}\sb2{dollar}-He and N{dollar}\sb2{dollar}-Ne interactions as models.;The excess and mixing excess thermodynamic properties of one and two component liquids of the rare gases and nitrogen are calculated using reliable two-body potential energies and statistical mechanical perturbation theory. For the most part, the deviations with respect to experiment are large; in the case of mixing excess properties, the discrepancies are partly due to the lack of agreement between the experimental and calculated excess properties of the pure components. The deviations from experiment can be largely attributed to the neglect of non-additive many-body contributions to the potential energy in the two-body intermolecular potential models employed.;A density dependent "effective" many-body intermolecular potential is developed for pure liquid Ar by modifying the best available two-body Ar-Ar potential energy; the adjustable parameters in the model are fixed by requiring agreement between the excess Helmholtz energy predicted by perturbation theory and the experimental values. The "effective" many-body potential energy model successfully predicts the remaining excess thermodynamic functions and the pressure.



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