Generalized Method for Charge-Transfer Equilibration in Reactive Molecular Dynamics

Area of Science:

• Computational Materials Science
• Surface Science
• Chemical Physics

Background:

• Existing variable charge models in reactive molecular dynamics often impose artificial global charge transfer, impacting the accuracy of surface process simulations.
• This limitation, stemming from approximations of systems as ideal metals, affects simulations of adsorption, desorption, deposition, and sputtering.
• Previous attempts to address this include split charge variants and models based on density functional theory, with varying degrees of success.

Purpose of the Study:

• To review and assess the applicability of the charge equilibration (QEq) and charge transfer quasi-potential (QTPIE) models for surface interaction studies.
• To propose a revised and generalized model for charge transfer equilibration in reactive molecular dynamics simulations.
• To introduce a novel mirror boundary condition to enhance the efficiency of surface investigations.

Main Methods:

• Evaluation of existing QEq and QTPIE models for their suitability in simulating surface interactions.
• Development of the charge-transfer equilibration (QTE) model, based on equilibrating charge-transfer variables and locally constraining split charge transfer.
• Implementation of an extended Lagrangian method for a formalism based solely on atomic charges and a mirror boundary condition.

Main Results:

• The proposed QTE model effectively constrains split charge transfer without requiring bond hardness parameters, offering a more physically realistic approach.
• The formalism derived using an extended Lagrangian method provides a robust framework based on atomic charges.
• The mirror boundary condition is shown to accelerate surface investigations in simulations.

Conclusions:

• The developed QTE model offers a significant improvement over traditional variable charge models for reactive molecular dynamics.
• The QTE model accurately describes various materials and surface phenomena, overcoming limitations of previous methods.
• The proposed methods facilitate more appropriate and efficient simulations of complex surface processes.