Anisotropic potential energy function

It has become attractive to consider a CG particle as ellipsoid because this treatment can give a reasonable approximation to the anisotropic nature of a cluster of atoms. The Gay-Beme anisotropic potential [55, 56] is actually based on a Gaussian-overlap potential [57], and in this work the Gay-Beme anisotropic potential energy function [/qb is represented by the functional form ... 

A very useful development of water/metal potential energy functions, which takes into account the anisotropic nature of the water/metal interactions, has been recently presented by Zho and Philpott." They used a fit to the ab initio binding energy of water on several metal surfaces and applied some simplifying assumptions to develop potentials for the inter-... 

Zhu and Philpott" employed a combination of relatively simple anisotropic and isotropic pairwise additive potential energy functions for a number of metal surfaces. They also provide a collective version of their potentials. 

The dispersion force in particular often has a large isotropic component, and in large or non-polar molecules, the isotropic terms may dominate the attractive forces. On the other hand, the repulsive force is determined by the shape of the molecule and tends to be very anisotropic. Even so, the repulsive wall is most important at low values of R, just as in the diatomic potential energy function. At high R, the anisotropic terms can often be ignored. 

Various models proposed may not account for all these experimental facts. The Keating [20] and Bottcher [21] evaluation does not account for such a variety of behavior. Goossens [22] proposed the chiral nematic structure as the result of an anisotropic dispersion energy between chiral mesogens, and predicts for thermotropic LCs a pitch that is essentially independent of temperature. Lin-Liu et al. [23] developed a theory that accounts for all the above-stated temperature effects. The temperature dependence of the pitch is determined by the shape and position of the intermolecular potential as a function of the intermolecular twist... 

In order to limit the total number of interactions exp>erienced by each molecule in a computer simulation, the potential energy is usually truncated so that a molecule s interaction range is finite. For example, the ordinary (spherical) Lennard-Jones potential is truncated at about 2.5cr the interactions between all molecules separated by more than this distance are weak enough to be neglected. In order to maintain conservation of energy, an anisotropic potential function should be truncated at an equipotential surface. However, if the potential is not too anisotropic, truncation at a fixed distance leads to only minor effects on energy conservation. ... 

In the molecular dynamics and Monte Carlo simulations which are the source of the results described herein, the overall potential energy surface was assumed to be a pairwise sum of two-body interactions. The Ar-Ar and Kr-Kr pair potentials were represented by the accurate functions determined by Aziz and Slaman, while the Ar-SF5 and Kr-SFg interactions were represented by the detailed anisotropic functions determined by Pack et alJ Although three-body forces may not be negligible in these systems, we doubt that their effects are larger than those of the uncertainties in our knowledge of the Rg-SF two-body potentials. 

---