Relativistic theory of the magnetic shielding constant:: a Dirac–Fock finite perturbation study

Four-component relativistic theory of the magnetic shielding constant is presented, based on the matrix Dirac–Fock finite perturbation method and implemented for numerical calculations with the MOLFDIR program. In contrast to the non-relativistic and quasi-relativistic formalisms, the shielding constant is written as a single term. Our formulation avoids explicit use of the positron states, in contrast to the conventional sum-over-states formalism. The magnetic shielding constants of the noble gas atoms, He through Xe, and those of H2, HF and HCl are calculated and compared with values obtained in non-relativistic calculations.