Quadratic response calculations of the electronic spin-orbit contribution to nuclear shielding tensors

The electronic spin-orbit contribution to nuclear magnetic shielding tensors, which causes the heavy-atom chemical shift of the shielding of light nuclei in the vicinity of heavy elements, is calculated as a sum of analytical quadratic response functions. We include both the one- and two-electron parts of the spin-orbit Hamiltonian and consider the interaction with both the Fermi contact and the spin-dipolar mechanisms. Ab initio calculations at the SCF and MCSCF levels are presented for the H1 and C13 shielding tensors in the hydrogen and methyl halides. The applicability of different approximations to the full spin-orbit correction is discussed, and the calculated results are compared with experimental data, where available.