Towards a New Perturbation Theory of Molecular Liquids

TL;DR

This paper introduces a new perturbation theory for molecular liquids that simplifies the calculation of thermodynamics by focusing on inter-atomic potentials and shows promising results at low densities.

Contribution

It proposes a novel splitting of site-site potentials to develop a perturbation theory that accurately predicts thermodynamics of molecular fluids at low densities.

Findings

Theory accurately predicts thermodynamics of hard sphere chain fluids.

Results agree well with computer simulations for carbon dioxide.

Approach simplifies calculations by excluding intra-atomic potentials.

Abstract

First steps towards developing a new perturbation theory for molecular liquids are taken. By choosing a new form of splitting the site-site potential functions between molecules, we will get a set of atomic fluids as the reference system with known structure and thermodynamics. The perturbative part of the potential function is then expanded up to two terms. The excess Helmholtz free energy of the system is then obtained for three computable contributions. The derivation shows that the excess Helmholtz free energy has nothing to do with intra-atomic potentials, all contributions come merely from inter-atomic potentials. Then it is applied to compute the thermodynamics of two systems; hard sphere chain and carbon dioxide molecular fluids. The results compared with the computer simulation data show that the theory works well at low densities.