Direct perturbation theory of magnetic properties and relativistic corrections for the point nuclear and Gaussian nuclear models

Starting from the Levy-Leblond equation, which is the four-component nonrel ativistic limit of the Dirac equation, a direct perturbation theory of magn etic properties and relativistic corrections is developed and implemented f or point-charge and finite nuclei. The perturbed small components are regul arized by projecting them onto an auxiliary small-component basis of Gaussi an functions. The relevant operators and matrix elements are derived for th e point-nuclear and Gaussian nuclear models. It is demonstrated how the usu al paramagnetic spin-orbit, Fermi-contact, and spin-dipole integrals of Ram sey's theory can be evaluated in the same manner as field and field-gradien t integrals-that is, as derivatives of potential-energy integrals. A few il lustrative calculations are performed. (C) 2001 American Institute of Physi cs.