Fourth-rank hypermagnetizability of medium-size planar conjugated molecules and fullerene

The fourth-rank hypermagnetizability tensor of a series of planar conjugated molecules—i.e., aromatic naphthalene, nonaromatic borazine, antiaromatic flattened cyclo-octatetraene, pentalene, indacene, and the 60-carbon fullerene,—has been evaluated at the coupled Hartree-Fock level of accuracy, within the conventional common-origin approach, via extended Gaussian basis sets. The theoretical predictions indicate that antiaromatic molecules are characterized by out-of-plane hypermagnetizability components much bigger than benzene’s. The fullerene cage has a hypermagnetizability exceeding that of planar aromatics by three orders of magnitude. However, the experimental determination of the hypermagnetizabilities constitutes a big challenge. Chemically substituted carbon clusters seem good candidates for detection of cubic magnetic response. Understanding of the calculated hypermagnetizabilities is eased by plots of the differential electron density induced by the applied field. It is found that a strong magnetic field perpendicular to the plane of antiaromatic molecules causes a distortion of the electron charge density, which tends to break C-C double bonds. This charge stretching has a dynamical origin and may be qualitatively explained as a feedback effect due to the Lorentz force acting on the electron current density.