Combination of the Perturbation Theory with Configuration Interaction Method

Present atomic theory provides accurate and reliable results for atoms with a small number of valence electrons. However, most current methods of calculations fail when the number of valence electrons exceeds four or five. This means that we can not make reliable predictions for more than a half of the periodic table. Here we suggest a modification of the CI+MBPT (configuration interaction plus many-body perturbation theory) method, which may be applicable to atoms and ions with filling d and f shells.