The square-well fluid: its properties and representation

Abstract

The compressibility factor, internal energy and radial distribution function in about 180 different thermodynamic states of systems of square wells with elongations λ = 1·4 and 1·6 are obtained by molecular-dynamics simulation. In this work, compressibility-factor data are used in a general procedure that analyses their functional dependences on temperature, density and elongation separately. The temperature dependence is described well by a polynomial in the reciprocal temperature, in agreement with perturbation theory. The empirical isothermal equation of state that we obtain contains up to the third virial coefficient correctly, and its density dependence is described well in terms of rational functions, quotients of polynomials of the same degree, which do not exceed 5. For constant density and temperature, the elongation dependence is also found to be described well by a polynomial.