Fisher-Watts potential

A comparison of the pairwise contribution to the Barker-Fisher-Watts potential with the Lennard-Jones potential for argon is shown in Figure 4.38. 

A notable example of a potential that does include many-body terms is the Barker-Fisher-Watts potential for argon, which combines a pairwise potential with an Axilrod-Teller triple... 

Comparison of the Lennard-]ones potential for argon with the Barker-Fisher-Watts pair potential kg is .mann s constant. 

All isothermal calculations discussed here employ Lennard-Jones potential functions and, unless otherwise stated, simulate free-boundary conditions. The neglect of three-particle interactions for a similar (Barker-Fisher-Watts) isolated pair potential has been shown to produce effects that are quite small for Ar systems. For clusters of more than three particles, the third-order potential energy terms 3 increase as the number of three-particle interactions increases. In the limit of zero temperature, where the third-order effects are most prevalent, 3 of the 13-particle Ar cluster (although already 60% of its bulk value) is less than 4.5% of the cluster s total potential energy. For a five-particle Ar cluster, 3 is less than 3% of the total potential energy. 

Fic. 6.S. The surface tension of argon (1), and its representation by a Lennard-Jones potential (2), by the pair potential of Barker, Fisher, and Watts (3al, and by this potential with a three-body correction (3b). 

Little is known concerning three body contributions to dynamic fluid properties. Fisher and Watts have calculated the self diffusion coefficient using the BFW pair potential without including the Axilrod-Teller interaction and obtained results similar to those for a Lennard-Jones fluid at the same densities (23). Schommers two dimensional Lennard-Jones plus Axllrod Teller simulations show significant three body effects on the velocity autocorrelation function however, the two dimensional self diffusion coefficient is little affected (16). Schommers is careful to point out, however, that results found in two-dimensional fluids do not necessarily extrapolate to three dimensions. 

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