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 $\frac{1}{r_{12}}$ 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, ${\mathrm{Fe}}^{18+}$, and ${\mathrm{Hg}}^{72+}$) and transition frequencies for $K$-hole states in ${\mathrm{Fe}}^{18+}$. 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.