Calculations of energy levels for atoms with several valence electrons

A new ab initio method for doing high-accuracy calculations for atoms with more than one valence electron is described. An effective Hamiltonian for the valence electrons is formed using many body perturbation theory for the residual core-valence interaction. The configuration interaction method is used then to find the energy levels of the atom. Application to thallium shows that this method gives an accuracy of about 0.5% for the ionization potential and a few tenths of a percent for the first few energy intervals. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 11, 844–848 (10 June 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.