Density pair correlation functions for molecular liquids: Approximations for polymers

We present a simple, physically motivated equation for the radial distribution function g(r) for molecular liquids, valid for polymers interacting via soft potentials. It is constructed to perform properly at low density for polyelectrolyte solutions. However, it also accounts for intermolecular correlations at both the molecular and monomer level, above those contained in the random phase approximation. We show that this theory reduces in various limits to some well-known polymer theories for g(r). In a preliminary analysis, we apply the equation for soft potentials to two very different systems: a solution of rod polyelectrolytes and a solution of flexible van der Waals chains. (C) 1998 American Institute of Physics. [S0021-9606(98)50147-X].