Optimized Valence Configurations and theF2Molecule

Abstract

The method of optimized valence configurations has been extended to include split-shell correlation and applied to the molecule ${\mathrm{F}}_2$. It is found (i) that consideration of the correlation of only the so-called valence electrons is sufficient to yield an accurate description of the chemical bond; (ii) that in accordance with the basic assumption of the method there exists a distinct separation in behavior between optimal configurations that represent the extra correlation resulting from molecular bonding and those that will ordinarily be associated with the correlation in separated atoms; and (iii) that the number of significant configurations of the first kind is small and readily obtainable by a sequence of limited multiconfiguration self-consistent field computations, followed by a single configuration interaction involving all new orbitals thus obtained, while those of the latter kind are indeed numerous but are easily accounted for by a suitable perturbation technique.