Thermodynamically self-consistent liquid state theories for systems with bounded potentials

TL;DR

This paper develops thermodynamically self-consistent liquid state theories for systems with bounded potentials, extending the SCOZA framework to arbitrary potentials and closure relations, with applications to the Gaussian core model.

Contribution

It introduces a generalized integro-differential formulation of SCOZA that is applicable to any potential and closure, beyond analytically solvable models.

Findings

MSA yields identical energy and virial expressions for GCM

SCOZA enforces thermodynamic consistency via a state-dependent function

The new formulation is fully numerical and broadly applicable

Abstract

The mean spherical approximation (MSA) can be solved semi-analytically for the Gaussian core model (GCM) and yields - rather surprisingly - exactly the same expressions for the energy and the virial equations. Taking advantage of this semi-analytical framework, we apply the concept of the self-consistent Ornstein-Zernike approximation (SCOZA) to the GCM: a state-dependent function K is introduced in the MSA closure relation which is determined to enforce thermodynamic consistency between the compressibility route and either the virial or energy route. Utilizing standard thermodynamic relations this leads to two different differential equations for the function K that have to be solved numerically. Generalizing our concept we propose an integro-differential-equation based formulation of the SCOZA which, although requiring a fully numerical solution, has the advantage that it is no longer restricted to the availability of an analytic solution for a particular system. Rather it can be used for an arbitrary potential and even in combination with other closure relations, such as a modification of the hypernetted chain approximation.