Dirac–Fock calculations of magnetic shielding constants: hydrogen molecule and hydrogen halides

Proton magnetic shielding constants of HX (X=H, F, Cl, Br, I) are calculated based on the Dirac–Fock finite perturbation (DF-FP) method. The results are in good agreement with experiments: the halogen dependence of the proton chemical shifts is well reproduced. The Gordon decomposition for the magnetic shielding constant gives results closely parallel to the lowest-order (c−2) terms in the traditional quasi-relativistic theories; the so-called diamagnetic, paramagnetic, spin–dipolar, and Fermi-contact terms. This decomposition shows that the Fermi-contact term is the most important origin of the relativistic effect on the chemical shift, as is well known in the quasi-relativistic theories.