The energy change occurring by perturbing a closed-shell molecule, either fixed in space or randomly tumbling, by a uniform external magnetic field has been expressed in terms of the magnetically induced Lorentz force density, which, at difference with previously introduced energy-based quantities, is independent of the point-of-view. The divergence of the isotropically averaged magnetically induced Lorentz force density allows for a local definition of diamagnetic and paramagnetic responses and enables us to distinguish aromatic, antiaromatic, and non-aromatic molecules, as shown by calculations on benzene, cyclooctatetraene, and borazine. The isotropically averaged magnetically induced Lorentz force density turns out very similar to the gradient of the electron density. This similarity is justified in terms of the current knowledge on the current density. A way is opened for an insightful and simplified topological characterization of molecular electronic structure via the magnetic response.
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