The Quantum Theory of Atoms in Molecules in Condensed Charge Density Space

TL;DR

This paper introduces a new 2D space called gradient bundle condensed charge density to better understand chemical regions in electron charge density, addressing debates about bond critical points and paths.

Contribution

It maps the gradient field of electron density onto a 2D space, revealing correlations with chemical significance and redefining bond regions in quantum chemistry.

Findings

Maxima in the new space often correspond to bond paths in electron density

The approach clarifies the chemical significance of bond critical points

Addresses concerns about the interpretation of bond paths in QTAIM

Abstract

By leveraging the fundamental doctrine of The Quantum Theory of Atoms in Molecules---the partitioning of the electron charge density ($\rho$) into regions bounded by surfaces of zero flux---we map the gradient field of $\rho$ onto a 2D space called the gradient bundle condensed charge density ($\cal{P}$). The topology of $\cal{P}$ appears to correlate with regions of chemical significance in $\rho$. The bond wedge is defined as the image in $\rho$ of the basin of attraction in $\cal{P}$, analogous to the Bader atom, which is the basin of attraction in $\rho$. A bond bundle is defined as the union of bond wedges that share interatomic surfaces. We show that maxima in $\cal{P}$ typically map to bond paths in $\rho$, though this is not necessarily always true. This observation addresses many of the concerns regarding the chemical significance of bond critical points and bond paths in The Quantum Theory of Atoms in Molecules.