Full four-component relativistic calculations of NMR shielding and indirect spin-spin coupling tensors in hydrogen halides

Various methods for the inclusion of relativistic effects in the calculation of NMR parameters are discussed. Benchmark values for the NMR shieldings and indirect nuclear spin–spin coupling tensors for the hydrogen halides are calculated using the four-component relativistic random phase approximation method. Apart from recovering the well-known trend of increasing hydrogen isotropic shielding going from HF to HI, we also find a large effect on the anisotropy that decreases along this series. Inclusion of spin-orbit coupling in a nonrelativistic formalism suffices to recover both effects on the hydrogen shieldings but fails to reproduce the much larger effect on the halogen shieldings. This effect can be explained by considering the relativistic mass-velocity operator that contains correction terms to the nonrelativistic magnetic field operators. We recommend routine inclusion of the one-electron spin-orbit correction in calculations of hydrogen shieldings for hydrogens bonded to heavy atoms. For the heavy nucleus shielding one should include an additional mass-velocity correction. The relativistic effect on the indirect nuclear spin–spin coupling tensor is large and affects mainly the isotropic values; the effect on the anisotropy is small.