Comparative Analysis of Molecular Dynamics and Method of Moments in Two-Dimensional Concentric Circular Layers

TL;DR

This study compares molecular dynamics simulations and the method of moments to analyze a classical two-dimensional Coulomb plasma on concentric circular layers, revealing conditions where both methods agree on thermodynamic averages.

Contribution

It introduces a protocol for comparing MD and MoM in Coulomb systems and identifies parameter regimes with consistent results between the two methods.

Findings

MD and MoM agree for certain coupling parameters and charge ratios

The system's thermodynamic averages depend on coupling and charge ratio

A comparison protocol is established for Coulomb systems on layered geometries

Abstract

In this manuscript, we undertake an examination of a classical plasma deployed on two finite co-planar surfaces: a circular region $\Omega_{in}$ into an annular region $\Omega_{out}$ with a gap in between. It is studied both from the point of view of statistical mechanics and the electrostatics of continua media. We employ a dual perspective: the first one is by using Molecular Dynamics (MD) simulations to find the system's positional correlation functions and velocity distributions. That by modeling the system as a classical two-dimensional Coulomb plasma of point-like charged particles $q_1$ and $q_2$ on the layers $\Omega_{in}$ and $\Omega_{out}$ respectively with no background density. The second one corresponds to a finite surface electrode composed of planar metallic layers displayed on the regions $\Omega_{in}$, $\Omega_{out}$ at constant voltages $V_{in}$, $V_{out}$ considering axial symmetry. The surface charge density is calculated by the Method of Moments (MoM) under the electrostatic approximation. Point-like and differential charges elements interact via a $1/r$ - electric potential in both cases. The thermodynamic averages of the number density, and electric potential due to the plasma depend on the coupling and the charge ratio $\xi=q_1/q_2$ once the geometry of the layers is fixed. On the other hand, the fields due to the SE depend on the layer's geometry and their voltage. In the document, is defined a protocol to properly compare the systems. We show that there are values of the coupling parameter, where the thermodynamic averages computed via MD agree with the results of MoM for attractive $\xi=-1$ and repulsive layers $\xi=1$. Keywords: molecular dynamics, method of moments, Coulomb systems, long-range interaction.