Self-contained equilibrium theory for freely jointed Lennard-Jones chain fluids and similar models

Abstract

On the basis of the van der Waals picture and an extension of the Weeks-Chandler-Andersen prescription, it is assumed that the average monomer-monomer radial distribution function of the freely jointed Lennard-Jones (LJ) chain fluid can be approximated by that of a hypothetical reference chain fluid in which the interatomic forces are entirely repulsive and identical to the repulsive forces generated by the LJ potential. The structural information for the reference chain system is approximated using the cavity correlation function of freely jointed hard sphere rings with an appropriately chosen hard sphere diameter. It is found that both the virial pressure and the excess internal energy obtained from the energy equation are quantitatively accurate at high densities and temperature. The method and analytical expressions used here employ no simulation input and are all relevant not only for an LJ potential but also any intermonomer potential with steep short range repulsion and longer range attraction.