Real space electrostatics for multipoles. III. Dielectric Properties

TL;DR

This paper analyzes how new real-space electrostatic methods for multipoles affect the dielectric properties of fluids, including corrections needed for accurate measurement of dielectric constants and susceptibilities.

Contribution

It derives correction formulas for dielectric properties using the new real-space multipole methods, extending understanding of screening in dipolar and quadrupolar fluids.

Findings

Derived correction formulas for dielectric constants and susceptibilities.

Showed how geometric factors influence charge screening.

Validated methods through analysis of ion interactions.

Abstract

In the first two papers in this series, we developed new shifted potential (SP), gradient shifted force (GSF), and Taylor shifted force (TSF) real-space methods for multipole interactions in condensed phase simulations. Here, we discuss the dielectric properties of fluids that emerge from simulations using these methods. Most electrostatic methods (including the Ewald sum) require correction to the conducting boundary fluctuation formula for the static dielectric constants, and we discuss the derivation of these corrections for the new real space methods. For quadrupolar fluids, the analogous material property is the quadrupolar susceptibility. As in the dipolar case, the fluctuation formula for the quadrupolar susceptibility has corrections that depend on the electrostatic method being utilized. One of the most important effects measured by both the static dielectric and quadrupolar susceptibility is the ability to screen charges embedded in the fluid. We use potentials of mean force between solvated ions to discuss how geometric factors can lead to distance-dependent screening in both quadrupolar and dipolar fluids.