Size-extensive polarizabilities with intermolecular charge transfer in a fluctuating-charge model

TL;DR

This paper introduces a fluctuating-charge model that accurately predicts size-extensive polarizabilities while permitting intermolecular charge transfer, addressing previous overestimations in large systems.

Contribution

It demonstrates a new approach that maintains size-extensivity and charge transfer capabilities in fluctuating-charge models by incorporating charge conservation terms.

Findings

Achieves linear-scaling polarizabilities with external electric field coupling.

Maintains correct translational symmetries of dipole moment and polarizability.

Addresses overestimation issues in large molecular systems.

Abstract

Fluctuating-charge models have been used to model polarization effects in molecular mechanics methods. However, they overestimate polarizabilities in large systems. Previous attempts to remedy this have been at the expense of forbidding intermolecular charge-transfer. Here, we investigate this lack of size-extensivity and show that the neglect of terms arising from charge conservation is partly responsible; these terms are also vital for maintaining the correct translational symmetries of the dipole moment and polarizability that classical electrostatic theory requires. Also, QTPIE demonstrates linear-scaling polarizabilities when coupling the external electric field in a manner that treats its potential as a perturbation of the atomic electronegativities. Thus for the first time, we have a fluctuating-charge model that predicts size-extensive dipole polarizabilities, yet allows intermolecular charge-transfer.