Electric dipole polarizabilities of the halogen atoms in P-2(1/2) and P-2(3/2) states: Scalar relativistic and two-component configuration-interaction calculations

A study of the influence of spin-orbit coupling and dynamical electron correlation on the polarizabilities of the halogen atoms in a variational treatment is presented. It is shown that for the heavier homologs it is necessary to replace the averaged values by individual component polarizabilities for the J=3/2 and J=1/2 atomic states due to the large spin-orbit coupling. A high level of correlation treatment by large-scale direct configuration interaction with up to quadruple excitations is maintained throughout. We, furthermore, put our relativistic two-component approach to the test by evaluating the change of picture effect on the polarizability values of the astatine atom arising from the neglect of a unitary transformation of the property operator to an approximate relativistic theory.