  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.
