Weeks-Chandler-Andersen system

Thermodynamics of the Weeks-Chandler-Andersen System Inherent Structure of Two-Dimensional Liquids Statistical Geometry of the Weeks-Chandler-Andersen System... 

D. Statistical Geometry of the Weeks-Chandler-Andersen System... 

As we have already pointed out, the theoretical basis of free energy calculations were laid a long time ago [1,4,5], but, quite understandably, had to wait for sufficient computational capabilities to be applied to molecular systems of interest to the chemist, the physicist, and the biologist. In the meantime, these calculations were the domain of analytical theories. The most useful in practice were perturbation theories of dense liquids. In the Barker-Henderson theory [13], the reference state was chosen to be a hard-sphere fluid. The subsequent Weeks-Chandler-Andersen theory [14] differed from the Barker-Henderson approach by dividing the intermolecular potential such that its unperturbed and perturbed parts were associated with repulsive and attractive forces, respectively. This division yields slower variation of the perturbation term with intermolecular separation and, consequently, faster convergence of the perturbation series than the division employed by Barker and Henderson. 

Most investigations in this area have been concerned with the Weeks-Chandler-Andersen division of the potential. For the molecular potential, the reference system is defined by... 

Although a large nrunber of theoretical approaches can be used to describe 2D Letmard-Jones systems, the Reddy-O Shea and the Cuadros-Mulero expressions for the equation of state are the most usefril from a practical point of view. In particular, the Cuadros-Mulero equation is the simplest expression and can be easily applied over a wide range of temperatures and densities. Moreover, it is based on the Weeks-Chandler-Andersen perturbation theory, thus permitting the study of the effects of the intermolecular repulsive and atlractive forces. 

The cluster expansions in this section are of the most primitive kind in the sense that they give A and the correlation functions relative to the corresponding functions for a reference system of noninteracting particles. Stell and Lebowitz have shown how to carry analogous procedures through for arbitrary reference systems, such as a suitable assembly of hard spheres. Other resummations and optimizations aimed at achieving better convergence of cluster series have been studied intensively by Andersen, Chandler, and Weeks. ... 

---