The dissociation catastrophe in fluctuating-charge models and its implications for the concept of atomic electronegativity

TL;DR

This paper introduces a reformulation of the QTPIE fluctuating-charge model that clarifies the concept of atomic electronegativity by distinguishing intrinsic atomic properties from environmental effects, improving understanding of charge dissociation.

Contribution

The authors reformulate the QTPIE model in terms of atomic charges, revealing two types of electronegativities and addressing dissociation issues in fluctuating-charge models.

Findings

Reformulation of QTPIE in atomic charges

Identification of two types of atomic electronegativities

Improved dissociation behavior in fluctuating-charge models

Abstract

We have recently developed the QTPIE (charge transfer with polarization current equilibration) fluctuating-charge model, a new model with correct dissociation behavior for nonequilibrium geometries. The correct asymptotics originally came at the price of representing the solution in terms of charge-transfer variables instead of atomic charges. However, we have found an exact reformulation of fluctuating-charge models in terms of atomic charges again, which is made possible by the symmetries of classical electrostatics. We show how this leads to the distinguishing between two types of atomic electronegativities in our model. While one is a intrinsic property of individual atoms, the other takes into account the local electrical surroundings. This suggests that this distinction could resolve some confusion surrounding the concept of electronegativity as to whether it is an intrinsic property of elements, or otherwise.