Weeks-Chandler-Anderson

Figure A3.1.1. Typical pair potentials. Illustrated here are the Lennard-Jones potential, and the Weeks-Chandler- Anderson potential, which gives the same repulsive force as the Leimard-Jones potential.

Note that the binary HMSA [60] scheme gives the solute-solvent radial distribution function only in a limited range of solute-solvent size ratio. It fails to provide a proper description for such a large variation in size. Thus, here the solute-solvent radial distribution function has been calculated by employing the well-known Weeks-Chandler-Anderson (WCA) perturbation scheme [118], which requires the solution of the Percus-Yevick equation for the binary mixtures [119]. 

We turn now to a discussion of perturbation theories based upon extensions of the Barker-Henderson and Weeks-Chandler-Anderson theories to interaction site potentials. Such theories seek to treat the properties of the fluid as a perturbation about a reference fluid with anisotropic repulsive forces only. The theories have been formulated both explicitly in terms of division of the site-site potential into reference and perturbation potentials (Tildesley, Lombardero et al. )... 

Whereas in principle, there are numerous ways to decompose the LJ interaction, conventionally two popular methods exist Barker-Henderson (BH) method (Barker and Henderson, 1967) and Weeks-Chandler-Anderson (WCA) method (Weeks et al., 1971) as schematically depicted in Fig. 8A and B, respectively. For instance, in BH method the two complementary parts follow (Barker and Henderson, 1967)... 

The attractive contributions for, for example, a Lennard-Jones (LJ) fluid, were modeled with the cut-shifted Lennard-Jones (CSLJ) potential, split according to the Weeks-Chandler-Anderson... 

For Lennard-Jones (LJ) and similar fluids, the first step toward the development of appropriate expressions is the decomposition of the fluid-fluid potential into repulsive and attractive terms. The Weeks-Chandler-Anderson (WCA) division is usually used [259], according to which the attractive part of the Lennard-Jones potential is given by... 

The two most commonly used procedures for the division of the pair potentials into the reference and the perturbation parts have been proposed by Barker and Henderson (BH) (19) and Chandler, Weeks, and Anderson (CWA) (23). Both procedures have been found to be equally satisfactory and the BH scheme is used here because of its simplicity. The division of the pair potential into repulsive and attractive parts, according to the BH scheme, is... 

The pseudo parameters of the HSE theory are derived from an equation of state expanded in powers of 1/kT about a hard-sphere fluid, as is developed by the perturbation theory. Consequently, it is reasonable to expect that procedures for defining optimal diameters for the perturbation theory should work well with the HSE procedure. The first portion of this chapter shows that this is indeed correct. The Verlet-Weis (VW) (5) modification of the Weeks, Chandler, and Anderson (WCA) (6) procedure was used here to determine diameters in a mixture of Len-nard-Jones (LJ) (12-6) fluids. These diameters then were used in the HSE procedure to predict the mixture properties. 

Weeks J, Chandler D and Anderson H C 1971 Role of repulsive forces in determining the equilibrium structure of simple liquids J. Chem. Phys. 54 5237... 

Weeks JD, Chandler D, Anderson HC (1971) Role of repulsive forces in detennining the equilibrium structure of simple liquids. J Chem Phys 54 5237 5247... 

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