Enhancement Of Diamagnetism By Momentum-Momentum Interaction: Application To Benzene

A well-known property of aromatic molecules is their highly anisotropic response to an external magnetic field: the magnetic susceptibility parallel to the field is generally much larger than the 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 show that if the interaction between the itinerant and bonding electrons is taken into account, a large enhancement of the molecule magnetic response takes place. The itinerant electrons are described by an extended Hubbard Hamiltonian with an effective momentum-momentum interaction between them which is mediated by the bonding electrons. For the particular case of a benzene molecule, our model reproduces the experimentally observed magnetic anisotropy.