Relativistic modification of asymptotic configuration interaction in the carbon isoelectronic sequence

Relativistic configuration interaction and many-body perturbation calculations have been performed on the J = 0 ground state of the carbon isoelectronic sequence up to Z = 106 (Z is nuclear charge) to establish quantitatively the way relativity alters the asymptotic configuration interaction. Although it is inappropriate to use relativistic many-body perturbation theory (RMBPT) based on a single-configuration reference state (1s(2)2s(2)2p(1/2)(2) J = 0) for low-Z members of the isoelectronic sequence due to strong mixing among several configuration states (i.e, quasi-degeneracy), the results of relativistic configuration interaction and many-body perturbation calculations demonstrate that RMBPT can be applied successfully to high-Z members in which strong mixing almost vanishes.