Generalized Method for Charge Transfer Equilibration in Reactive Molecular Dynamics

TL;DR

This paper introduces a new charge transfer equilibration (QTE) model for reactive molecular dynamics that improves the simulation of surface phenomena by addressing limitations of existing variable charge models.

Contribution

A generalized QTE model based on constrained charge transfer variables is proposed, enhancing the accuracy of surface process simulations in reactive molecular dynamics.

Findings

QTE model effectively describes surface interactions.

Mirror boundary condition accelerates surface investigations.

Model facilitates more accurate reactive MD simulations.

Abstract

Variable charge models (e.g., EEM, QEq, ES+) in reactive molecular dynamics simulations often inherently impose a global charge transfer between atoms (approximating each system as ideal metal). Consequently, most surface processes (e.g., adsorption, desorption, deposition, sputtering) are affected, potentially causing dubious dynamics. This issue is meant to be addressed by the ACKS2 and QTPIE model, which are based on the Kohn-Sham density functional theory as well as a charge transfer restricting extension to the QEq model (approximating each system as ideal insulator), respectively. In a brief review of the QEq and the QTPIE model, their applicability for studying surface interactions is assessed in this work. Following this reasoning, the demand for a revised generalization of the QEq and QTPIE model is proposed, called charge transfer equilibration model or in short QTE model. This method is derived from the equilibration of constrained charge transfer variables, instead of considering atomic charge variables. The latter, however, are obtained by a respective transformation, employing an extended Lagrangian method. We moreover propose a mirror boundary condition and its implementation to accelerate surface investigations. The models proposed in this work facilitate reactive molecular dynamics simulations which describe various materials and surface phenomena appropriately.