Calculations of energy levels for atoms with several valence electrons
Dzuba V.A., Flambaum V.V., Kozlov M.G.
A new ab initio method for the high-accuracy calculations of 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. 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 tenth of a percent for the first few energy intervals. PACS: 31.15.Ai, 31.15.Md