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A version of the configuration interaction (CI) method is developed whichtreats highly excited many-electron basis states perturbatively, so that theirinclusion does not affect the size of the CI matrix. This removes, at least inprinciple, the main limitation of the CI method in dealing with many-electronatoms or ions. We perform calculations of the spectra of iodine and its ions,tungsten, and ytterbium as examples of atoms with open $s$, $p$, $d$ and$f$-shells. Good agreement of the calculated data with experiment illustratesthe power of the method. Its advantages and limitations are discussed.

Combining configuration interaction with perturbation theory for atoms with large number of valence electrons