Electronic Wavefunctions for Atoms. III. Partition of Degenerate Spaces and Ground State of C

摘要

The atomic configurationhyphen;interaction (CI) expansion is expressed in terms of constituents which are invariant under linear transformations of the radial onehyphen;electron basis. For openhyphen;shell states, the degenerateLSspaces are partitioned into maximal Hartreendash;Fock (HF) noninteracting spaces and minimal HF interacting spaces. This particular partition is shown to improve considerably the convergence of the atomic CI expansion, and it may be applied to molecular CI expansions in terms of symmetry orbitals. An exhaustive calculation of the ground state of C is carried out. A wellhyphen;defined linear transformation of the radial onehyphen;electron basis is made in order to improve further the convergence of the CI series. The final 234hyphen;term CI expansion (formed from a determinantal space of dimension 4836) obtained with an optimized7s6p4d3fbasis, gives an energyEthinsp;equals;thinsp;minus;37.83378a.u.(C), accounting for more than 93percnt; of the correlation energy. The C wavefunction is believed to be expressed in its most rapidly convergent form. The advantages of the present approach to atomic CI calculations are discussed.