Modification of the Significant Structure Theory of Liquids for Argon at High Pressures and Temperatures

Abstract

The significant structure theory of liquids is applied to the shock and isothermal compression of argon. Three models and two types of intermolecular potential are considered. In Model 1, an Einstein oscillator model is used in the solid partition function. In Model 2, a Lennard-Jones and Devonshire cell model is used in the solid partition function. In Model 3, a cell model is used for the entire partition function (this version is independent of the significant structure theory). For the intermolecular potential, exp-6 and 12–6 are adopted separately with numerical parameters obtained from second virial coefficient and high-density shock wave experiments. The Einstein characteristic temperature and sublimation energy at absolute zero are calculated from the potential energy function based on the cell model. The experimental solidus is introduced for the molar volume of the solid. All the calculations are performed in a computer program without which analytical calculations are cumbersome or impossible. It is found that Model 1 with exp-6 potential provides the best fit to measurements. Calculated Hugoniot and isotherms agree well with experimental results.