Accounting for admixed configurations in the second order of perturbation theory for complex atoms

The method of accounting for the correlation effects, based on the combination of perturbation theory and superposition of configurations, is described. The method described is aimed at theoretical description of much more complex atoms and ions, having open nd(N) and/or nf(N) shells, where MBPT or its 1/Z version fail. In order to increase the convergency the transformed radial orbitals were used. The method was applied to calculate the energy levels of the configurations 1s(2)2s(2)2p(2) (Ar XIII and ions 8 less than or equal to Z less than or equal to 30), 1s(2)2s2p(3) and 1s(2)2p(4) (8 less than or equal to Z less than or equal to 30) as well as term energies of 3d(2) Fe VII and 3d(3) Fe VI. The examples studied show that the approach described allows fairly effectively to take into account the correlation effects while calculating the energy spectra of a large variety of atoms, containing open d shells.