Numerical methods of the preliminary evaluation of the role of admixed configurations in atomic calculations

Methods of the preliminary evaluations of the averaged energy correlation c orrections and averaged configuration mixing weights arising from the separ ate admired configurations are presented in this paper. These methods are b ased on the usage of the second order of the perturbation theory and analyt ical expressions of the sums of the squares of the interconfigurational mat rix elements and the averaged energy differences between configurations. Tw o possible ways to average these energy differences are discussed. Large nu mber of calculations for different atomic states shows a good agreement of the preliminary evaluations with averaged results from diagonalization of e nergy matrices. (C) 2001 Elsevier Science B.V. All rights reserved.