Enhancement of diamagnetism by momentum-momentum interaction: application to benzene

TL;DR

This paper introduces an extended Hubbard model for aromatic molecules, revealing that bonding electrons mediate an attractive momentum-momentum interaction that significantly enhances diamagnetism, aligning with experimental observations in benzene.

Contribution

It proposes a novel extended Hubbard model incorporating bonding electron interactions, explaining enhanced diamagnetism in aromatic molecules like benzene.

Findings

Bonding electrons mediate an attractive momentum-momentum interaction.

The model reproduces benzene's magnetic anisotropy with realistic parameters.

Enhanced diamagnetism is linked to electron interactions mediated by bonding electrons.

Abstract

A well-known property of aromatic molecules is their highly anisotropic response to the presence of an external magnetic field: the component of their magnetic susceptibility parallel to the field is generally much larger than the remaining in-plane components. This intriguing phenomenon is rationalized as a consequence of the delocalization of the itinerant electrons that populate the aromatic ring. In this work, we revisit the magnetism of aromatic molecules and propose an extended Hubbard model for the electrons in the aromatic ring that takes into account the interaction between them and the bonding electrons. We show that the bonding electrons play an important and overlooked role: they mediate an effective, attractive momentum-momentum interaction between the itinerant electrons, which promotes a strong enhancement in the magnetic response of the aromatic ring. For the particular case of benzene, we show that the experimentally observed magnetic anisotropy is recovered with realistic values of the coupling constants.