Routes to the density profile and structural inconsistency

TL;DR

This paper introduces an alternative density functional theory (DFT) approach using the LMBW equation that ensures consistency with the compressibility route and proposes an optimization scheme to minimize structural inconsistencies in inhomogeneous fluid modeling.

Contribution

It presents a novel DFT scheme based on the LMBW equation that aligns with the compressibility route and allows for structural inconsistency minimization via closure relations.

Findings

LMBW DFT achieves consistency with the compressibility route.

Structural inconsistency can be minimized through an optimization scheme.

Numerical results demonstrate the method's effectiveness for 2D Yukawa particles.

Abstract

Classical density functional theory (DFT) is the primary method for investigations of inhomogeneous fluids in external fields. It requires the excess Helmholtz free energy functional as input to an Euler-Lagrange equation for the one-body density. A variant of this methodology, the force-DFT, uses instead the Yvon-Born-Green equation to generate density profiles. It is known that the latter are consistent with the virial route to the thermodynamics, while DFT is consistent with the compressibility route. In this work we will show an alternative DFT scheme using the Lovett-Mou-Buff-Wertheim (LMBW) equation to obtain density profiles, that are shown to be also consistent with the compressibility route. However, force-DFT and LMBW DFT can both be implemented using a closure relation on the level of the two-body correlation functions. This is proven to be an advantageous feature, opening the possibility of an optimisation scheme in which the structural inconsistency between different routes to the density profile is minimized. (Structural inconsistency is a generalization of the notion of thermodynamic inconsistency, familiar from bulk integral equation studies.) Numerical results are given for the density profiles of two-dimensional systems of hard-core Yukawa particles with a repulsive or an attractive tail, in planar geometry.