Multiconfiguration relativistic Hartree-Fock-Roothaan theory for atomic systems

By using the expansion method, the multiconfiguration relativistic Hartree-Fock-Roothaan theory for atomic systems is presented. The matrix element for two-electron operators, such as 1r₁₂ or the Breit operator, is calculated by using tensor-recoupling-transformation techniques for the second-quantized operators. The theory is tested in the calculation of term energies for oxygenlike atomic systems (O, Fe¹⁸⁺, and Hg⁷²⁺) and transition frequencies for K-hole states in Fe¹⁸⁺. It is shown that calculated term energies and transition frequencies agree well with experiment. The role of the electron correlation effects and the relativistic effects in each system is also discussed.