RELATIVISTIC THEORY OF THE MAGNETIC SHIELDING CONSTANT - A DIRAC-FOCKFINITE PERTURBATION STUDY

Four-component relativistic theory of the magnetic shielding constant is presented, based on the matrix Dirac-Fock finite perturbation metho d and implemented for numerical calculations with the MOLFDIR program. In contrast so 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 convent ional sum-over-states formalism. The magnetic shielding constants of t he noble gas atoms, He through Xe, and those of H-2, HF and HCl are ca lculated and compared with values obtained in non-relativistic calcula tions. (C) 1998 Elsevier Science B.V.