Precision calculations of atoms with few valence electrons

Abstract

We discuss the possibility of using pair-equations for the construction of the effective Hamiltonian $H_{\mathrm{eff}}$ for valence electrons of an atom. The low-energy part of atomic spectrum is found by solving the eigenvalue problem for $H_{\mathrm{eff}}$. In this way it is possible to account efficiently for the valence-valence and core-valence correlations. We tested this method on a toy model of a four-electron atom with the core $1s^2$. The spectrum obtained with $H_{\mathrm{eff}}$ for two valence electrons is in a perfect agreement with the full configuration interaction for all four electrons.

Talk at the VI Fock school, Novgorod, Russia. 11 pages, 6 figures