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International audience; The fast interconnections of the presently available distributed platforms allow scientists to target highly complex problems by chaining software developed and maintained by experts of the relevant fields. A pillar of such cooperative endeavor in molecular and materials science and technologies is the so-called grid empowered molecular simulator that combines the expertise of molecular science theorists (electronic structure and nuclei dynamics) and experimentalists in order to build and validate ab initio models. This line has prompted an unprecedented level of data format standardization procedures, the bridging of high throughput and high performance platforms, the assemblage of ad hoc designed virtual experiments. In addition this approach has prompted the design and development of tools allowing the evaluation of the quality of the cooperative effort produced by the members of a given research community as well as its rewards to such effort through a credit economy is reported.

The frequency dependence of the dipole electric polarizability and electric shielding tensors of hydrogen and lithium nuclei in the LiH molecule has been studied via some approximations to the polarization propagator method, i.e., STA, TDA, and RPA, allowing for dipole length, velocity, acceleration, and mixed formalisms. The RPA nuclear electric shieldings are in a fairly good agreement with the corresponding experimental data, a discrepancy being observed for the parallel component at the Li nucleus.

By means of symmetry considerations it is shown that aromatic hydrocarbons, perturbed by a magnetic field perpendicular to the molecular plane, are characterized by an interatomic paramagnetic circulation of electrons, flowing around the highest symmetry axis, which is related to the nodal topology of the wave function. An actual calculation confirms that the field of quantum-mechanical current density presents an axial vortex due to σ electrons in benzene, which overcomes the diamagnetic π streamlines. The analysis of the orbital contributions to proton nuclear shielding reveals that σ electrons cause low field shifts, in the NMR spectrum, comparable in magnitude with those arising from π circulation. These results would imply the need for modifying some features of London's ring current model.

The singularities of the quantum-mechanical electron current density induced in a molecule by an external magnetic field are analyzed via the theory of the real autonomous systems of differential equations. Group-theoretical techniques, based on the idea of color symmetry, are developed, which predict the occurrence of singularities about molecular symmetry elements. Plots of induced electron current density have been obtained for the ethylene molecule through accurate coupled SCF calculations. The theoretical magnetic properties of ethylene obtained through this investigation are the most accurate reported so far.

A first‐order polarization propagator approximation has been adopted to compute the full nuclear spin–spin coupling tensors 1J(X–H) and 2J(H–H) in SiH4 and AlH−4. The higher efficiency of the computational scheme related to the propagator formalism, with respect to the conventional coupled Hartree–Fock method, has been proved. The diamagnetic spin‐dipolar term has been found to provide a larger contribution than the Fermi‐spin‐dipolar cross term to the anisotropy of 1J(X–H). Spin‐dipolar contributions are negligible and the bulk of the average coupling is determined by the Fermi contact term.

Coupled Hartree–Fock perturbation theory, within the framework of an accurate calculation, has been employed to visualize the electronic current density vector field induced by an external uniform magnetic field in the acetylene molecule. The current regime in a plane containing the molecular axis is rather different from those usually accounted for, evidencing the presence of a toroidal vortex in the CH bond. The maps are useful in rationalizing the experimentally observed proton and carbon NMR chemical shifts.

The diamagnetic spin‐orbit contribution to the nuclear spin–spin coupling constants of water has been calculated employing SCF wave functions of increasing accuracy. The results demonstrate that this term is small in the case of direct O–H average coupling constants. On the other hand, a significant contribution (≂−7 Hz) to geminal H–H coupling constant is found. The theoretical results are slightly affected by the characteristics of the basis set employed in the calculations.