Relativistic calculations for highly correlated atomic and highly charged ionic systems

The effect of electron correlations in many electron atoms or many electron atomic ions are discussed extensively based on the MultiConfiguration Dirac Fock (MCDF) calculations. In a precision atomic physics the relativistic treatment of the system is indispensable. The correlation effects and the relativistic effects are no more additive if one want to treat the many electron systems accurately. In the excited states, the single electron orbitals are modified in accordance with the vacancies near the atomic center. The electron correlations may be evaluated from the non-orthogonality of the single electron orbitals. Several examples have been given. The electronic configurations with the same total parities may interact each other even in the cases the constituent single electron orbitals have opposite parities. Such the configuration interactions may provide us with characteristic interference structures in the optical emission or absorption spectra. The anormally of the extreme ultra-violet optical emission spectra of highly charged tin ions has been illustrated as an example.