A relativistic C.I. study on the J = 1/2 even spectrum of Sr II

We present a method for performing relativistic CI calculations in ground and excited atomic and ionic levels. An electron occupying a relativistic shell nκ in a given electronic configuration is described by a single numerical four-component Dirac-Fock orbital having the same n and κ quantum numbers to those of the shell nκ. Application of this method yields estimates for the P(88741 cm-1) and the I.P. correlation energy (-30916 cm-1) for Sr II and for the total correlation energy in Sr III (-30916 cm-1). Core-valence correlation energies for the vertical strokecore 5s> (-4379 cm-1), vertical strokecore 6s> (-1191 cm-1) and vertical strokecore 13s> (-32 cm-1) levels have been calculated for Sr II. Estimates for the total relativistic, Breit, vacuum polarization and self energy corrections for these levels are also reported. Configurations in which the core is not fully occupied have been found to yield significant contributions to the correlation energies of both ground and excited levels. Our results show that full scale relativistic CI calculations using numerical four-component Dirac-Fock orbitals are feasible and provide a useful ab-initio tool for the investigation of atomic properties within the framework of fully relativistic theories. (orig.)