Simulation of Charged Systems in Heterogeneous Dielectric Media via a True Energy Functional

TL;DR

This paper derives a true energy functional for simulating charged systems in heterogeneous dielectrics, enabling more accurate molecular dynamics simulations of such systems, exemplified by ionic profiles near emulsion droplets.

Contribution

It introduces a true free energy functional for charged systems in heterogeneous dielectrics, facilitating advanced MD simulations without solving the Poisson equation directly.

Findings

Non-monotonic ionic profiles observed in low dielectric constant regions.

Development of a Car-Parrinello MD method for heterogeneous dielectric media.

Functional enables dynamic polarization charge density simulations.

Abstract

For charged systems in heterogeneous dielectric media, a key obstacle for molecular dynamics (MD) simulations is the need to solve the Poisson equation in the media. This obstacle can be bypassed using MD methods that treat the local polarization charge density as a dynamic variable, but such approaches require access to a true free energy functional; one that evaluates to the equilibrium electrostatic energy at its minimum. In this letter, we derive the needed functional. As an application, we develop a Car-Parrinello MD method for the simulation of free charges present near a spherical emulsion droplet separating two immiscible liquids with different dielectric constants. Our results show the presence of non-monotonic ionic profiles in the dielectric with lower dielectric constant.