Core-valence correlations for atoms with open shells

We present an efficient method of inclusion of the core-valence correlations into the configuration interaction (CI) calculations. These correlations take place in the core area where the potential of external electrons is approximately constant. A constant potential does not change the core electron wave functions and Green's functions. Therefore, all operators describing interaction of M valence electrons and N-M core electrons [the core part of the Hartree-Fock Hamiltonian VN-M, the correlation potential Sigma(1()r, r', E), and the screening of interaction between valence electrons by the core electrons Sigma(2)] may be calculated with all M valence electrons removed. This allows one to avoid subtraction diagrams which make accurate inclusion of the core-valence correlations for M > 2 prohibitively complicated. Then the CI Hamiltonian for M valence electrons is calculated using orbitals in complete VN potential (the mean field produced by all electrons); Sigma(1)+ Sigma(2) are added to the CI Hamiltonian to account for the core-valence correlations. We calculate Sigma(1) and Sigma(2) using many-body perturbation theory in which dominating classes of diagrams are included in all orders. We use neutral Xe I and all positive ions up to Xe VIII as a testing ground. We found that the core electron density for all these systems is practically the same. Therefore, we use the same Sigma(1) and Sigma(2) to build the CI Hamiltonian in all these systems (M= 1, 2, 3, 4, 5, 6, 7, 8). Good agreement with experiment for energy levels and Lande factors is demonstrated for all cases from Xe I to Xe VIII.