The electrostatic interaction of an external charged system with a metal surface: a simplified density functional theory approach

TL;DR

This paper introduces a simplified DFT method to calculate electrostatic interactions between charged systems and metal surfaces, neglecting non-local effects and assuming a non-overlapping electron density approximation.

Contribution

A new electrostatic DFT scheme is developed to model charged systems near metal surfaces, focusing on electrostatic interactions and linear metal response, exemplified with a Na+ cation.

Findings

Method successfully implemented computationally.

Applicable to charged atoms and molecules on metal surfaces.

Validated with Na+ cation example.

Abstract

As a first step to meet the challenge to calculate the electronic structure and total energy of charged states of atoms and molecules adsorbed on ultrathin-insulating films supported by a metallic substrate using density functional theory (DFT), we have developed a simplified new DFT scheme that only describes the electrostatic interaction of an external charged system with a metal surface. This purely electrostatic interaction is obtained from the assumption that the electron densities of the two fragments (charged system and metal surface) are non-overlapping and neglecting non-local exchange correlation effects such as the van der Waals interactions between the two fragments. In addition, the response of the metal surface to the electrostatic potential from the charged system is treated to linear order, whereas the charged system is treated fully within DFT. In particular, we consider the classical perfect conductor (PC) model for the metal response, although our formalism is not limited to this approximation. The successful computational implementation of this new methodology and the PC model is exemplified by the case of a Na$^{+}$ cation outside a metal surface.