The role of excluded volume in polyethylene intermolecular potentials

A number of common methylene–methylene intermolecular potentials are mapped onto effective hard monomer interactions. The potentials considered are of the united atom (UA), the anisotropic united atom (AUA), and the explicit atom (EA) types. The effective site diameter can be used as a means of comparison between these rather diverse potential functional forms. Although we have not attempted a complete survey of the literature, we find that there is a surprisingly wide range of hard site diameters predicted. The average diameter is 3.7 Å; the minimum, 3.4 Å; and the maximum, 3.9 Å. These are distressing findings in terms of predicting system properties such as the structure factor or the diffusion coefficient which sensitively depend upon excluded volume.