Alternative Technique for the Calculation of Single-Determinant Open-Shell SCF Functions Which Are Eigenfunctions of S2

Abstract

The most general possible restriction is developed such that a single‐determinant open‐shell SCF wavefunction shall be an eigenfunction of S 2 . A method of satisfying this restriction by partitioning of the variational basis set is given. The method is computationally distinct from the equivalence restriction procedure of Roothaan, but yields results equivalent to it. A pilot calculation on the 2 Σ + state of BO is carried out as an explicit example of the new method.