Francesco Ferdinando Summa

This work presents the theoretical background for the computation of nuclear magnetic shielding, nuclear hyperfine, and magnetizability tensors of paramagnetic molecules using a magnetically induced current density framework to account for both orbital and spin contributions. The resulting magnetizability tensor is fully consistent with the general Van Vleck formulation, recovering the temperature-dependent Curie contribution through the explicit integration of the magnetically induced spin current density. The methodology proposed herein provides a straightforward computational route that bypasses the complex evaluation of g-tensors and zero-field splitting Hamiltonians. While the theoretical framework is general, we present applications rooted in physically motivated approximations where scalar relativistic effects are incorporated through corrections based on the zeroth-order regular approximation Hamiltonian within the ground-state spin density. This approach combines a relativistic self-consistent field calculation for the ground-state spin density with a non-relativistic, origin-independent current density calculation for the orbital contribution. This hybrid strategy is shown to capture the heavy-atom light-atom effect in 1H and 13C shieldings, particularly in paramagnetic molecular systems containing transition metals up to the 3d series. By restricting the relativistic treatment to the spin density, where scalar relativistic effects are dominant, and neglecting such effects on the orbital contribution of light atoms, this method offers a good compromise between computational efficiency and accuracy for the characterization of large open-shell molecular systems.

Magnetically induced 3D current densities, net bond current strengths and divergence of the isotropically averaged Lorentz force density are used to characterize the magnetic response of giant I _h -fullerenes containing 240 and 540 carbon atoms.

A new method based on the solution of time-independent standard response equation has been developed for the calculation of spin-spin coupling density functions, entirely in the atomic orbital basis at both HF and DFT (GGA and hybrid GGA) level of theory. The study is not limited to the Fermi contact alone, but also includes all four Ramsey terms, which have sometimes been shown to be non-negligible. The current density induced by nuclear magnetic dipoles represents the leading motif followed in the development of the theory. A few molecules have been analyzed in detail. The mechanism of spin polarization can be visualized, and the distinction between through-space and through-bond interactions can now be understood in terms of all four Ramsey contributions.

Carboncone[1,3] (C ₈₀ H ₂₀ ) 25 Clar structures with 9 sextets each. Sextets can be located only in green (6 times) and blue (7 times) rings. A sextet is never found in empty rings.

Cationic hydrocarbon nanobelts were synthesized via the chemical oxidation of methylene-bridged [6]cycloparaphenylene ([6]MCPP). These species turned out to be remarkably stable in air, which enabled to uncover their unique properties.

A method for the calculation of divergenceless, magnetically induced quantum mechanical current densities in molecules that approximates the exact current is presented. This was achieved by adding to the calculated conventional current density, i.e., a current that typically has a non-zero divergence, a corrective term that is the negative of the irrotational field of its Helmholtz decomposition. The solenoidal field of the decomposition is the divergence-free current density, which is still an approximation of the exact current but which now satisfies the continuity requirement regardless of the quality of the basis set. Based on calculations performed on several simple molecules (LiH, H2O, benzene, and zethrene), adopting different kinds of low-level theoretical approaches, clear improvements are observed in the correspondence of vortices, sources, and sinks for which the conventional current density shows a lack of continuity. A little improvement is also observed for the calculated diagonal components of the magnetizability tensor.

Quantum chemical topology addresses the study of the chemical structure by applying the tools of differential topology to scalar and vector fields obtained by quantum mechanics. Here, the magnetically induced isotropically averaged Lorentz force density was computed and topologically analyzed for 11 small molecules. Critical points (attractors, repellers, and saddles) were determined and trajectories connecting the attractors computed. It is shown that kinds and numbers of the critical points are to some extent transferable in similar molecules. CC bonds of different orders are endowed with critical points of different kinds close to their center. The sum of topological indices of the isolated critical points is influenced by the presence of repellers on the outer part of the molecules.

Quantum chemical topology addresses the study of the chemical structure by applying the tools of differential topology to scalar and vector fields obtained by quantum mechanics. Here the magnetically induced isotropically averaged Lorentz force density has been computed and topologically analysed for 11 small molecules. Critical points (attractors, repellers and saddles) have been determined and trajectories connecting the attractors have been computed. It is shown that kinds and numbers of the critical points are rather transferable in similar molecules. CC bonds of different order are endowed with critical points of different kind close to their centre. The long range behaviour of the force allows understanding the value of the sum of topological indices of the isolated critical points.

Some years ago, Jishan Wu reported the synthesis of 8MC and 10MC, two homologues of the cyclopenta‐ring‐fused oligo(m‐phenylene) macrocycles mMC, each behaving as an annulene‐within‐an‐annulene (AWA). This was a surprising result as the AWA behavior is rare. Both molecules have a partial polyradical character, enforced by the quest for restoring some aromatic character of benzene rings. However, that restoration brings back some coupling between the two annulenes. Indeed, we found that the geometry and the magnetically induced currents indicate that, while 8MC does have an AWA character, this is not the case of the larger 10MC. Limitations of the design strategy of AWA molecules should be taken into account in future attempts to prepare novel large coronenes.