Theoretical Study of the F2 Molecule Using the Method of Optimized Valence Configurations

Abstract

The method of optimized valence configurations (OVC) is used to study the potential curve for the ground state of the F₂ molecule. All the important electron correlation‐effects within and between various molecular shells are investigated via the multiconfiguration self consistent field (MCSCF) process. It is found that, consistent with the philosophy of the OVC method, these effects fall into two distinct categories: (1) the molecular correlation, which vanishes when the molecule dissociates into the constituent atoms, and (2) the atomic correlation, which passes asymptotically to that for the atoms. The very weak interdependence or ``coupling'' of the two correlation types results in considerable computational simplification by permitting MCSCF calculations to be performed on groups, consisting of a comparatively small number of configurations, and the evaluation of their respective contributions to the bonding interaction by a simple summation in the spirit of pair theory. Such calculations on F₂ yield a potential curve which is very similar to the one derived from experiment. Our calculated values of the spectroscopic constants D_e, ω_e, R_e are, respectively, 1.67 eV, 942 cm⁻¹, 2.67 bohr. These are in good agreement with the corresponding experimental values 1.68 eV, 932 cm⁻¹, 2.68 bohr. General rules are given for applying this procedure to other molecular systems.