Hard and Soft-Core Equations of State for Simple Fluids. IX. Soft-Core Equations of State and Loci of C_p Extrema

Abstract

Loci of C_p extrema along isotherms are constructed for model soft-core equations of state, parameterized by an exponent N(= 3/n, where n is the repulsive potential exponent) and a softening temperature T_s . Generally the loci exhibit two branches whose geometry depends on T_s and N. In soft-core type behaviour, a locus of C_p maxima commences at the critical point and terminates on the temperature axis at a temperature T_n where the second virial coefficient has a point of inflexion, and the second branch is located at higher pressures and temperatures. In hard-core type behaviour, a locus of C_p maxima commences at the critical point and turns into a locus of minima before crossing the fusion curve, whereas the second branch, which terminates at T_D , is generally a locus of minima lying at high pressures and temperatures. The values of T_s and N at which the geometry of the loci changes is studied in detail.