Combined configuration-superposition and many-particle perturbation calculations for atoms with two valence electrons

A new high-precision method is used to calculate the characteristics of atoms with two valence electrons. An effective Hamiltonian for the valence electrons is formulated by many-particle perturbation theory with respect to the residual interaction of the valence electrons with the core. The configuration-superposition method is then used to find the energy levels of the atom. The application of the combined method to divalent calcium, strontium, barium, and ytterbium atoms shows that the ionization potential is obtained within 0.5% error limits. The precision attained for the first few lowest levels of the energy spectra is significantly higher than is obtained by configuration-superposition calculations alone. Zh. éksp. Teor. Fiz. 111, 838–846 (March 1997)