Magnetic susceptibility and nuclear shielding

Magnetic susceptibility and nuclear magnetic shielding of a chosen nucleus I, in the presence of an external weak, homogeneous electric field E may be expanded as (3)... 

The third-rank diamagnetic and paramagnetic contributions to electric field dependent magnetic susceptibility and nuclear magnetic shielding, to first order in... 

An important aspect of magnetic susceptibility and nuclear magnetic shielding is that they can theoretically be expressed as sums of diamagnetic (diatropic) and paramagnetic (paratropic) current distributions. For a closed-shell molecule with N electrons, the total first-order induced current density at point r is [33-35] ... 

Direct ab initio calculations of magnetic parameters are usually restricted to the magnetic susceptibility and the nuclear shielding tensors. Only recently have calculations of the g-tensor appeared. 

Calculations of the dependence of the nuclear shielding on bond length in H2 appeared some years ago,56 and the authors have recently calculated the magnetic susceptibility using their wavefunction and compared it with the KW function.57 Several important predictions of this work remain to be experimentally verified. 

Finally, in the third section of this paper, we describe a semiempirical atom dipole model that allows a reliable prediction of molecular electric dipole and quadrupole moments, diamagnetic susceptibilities, and diamagnetic nuclear shieldings. A set of localized bond and atom values are developed for the individual diagonal elements in the total molecular magnetic susceptibility tensor. 

N. F. Ramsey, Phys. Rev., 78, 699 (1950). Magnetic Shielding of Nuclei in Molecules. N. F. Ramsey, Phys. Rev., 86, 243 (1952). Chemical Effects in Nuclear Magnetic Resonance and in Diamagnetic Susceptibility. 

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