LOCALIZE

The occupied eigenvectors are transformed into a localized [38] set of M.O.s by a series of 2 by 2 rotations which maximize <ψ4>. The value of 1/<ψ4>  is a direct measure of the number of centers involved in the MO: thus, the value of 1/<ψ4>  is 2.0 for H2, 3.0 for a three-center bond and 1.0 for a lone pair. Higher degeneracies than allowed by point group theory are readily obtained. For example, benzene would give rise to a 6-fold degenerate C-H bond, a 6-fold degenerate C-C sigma bond and a three-fold degenerate C-C pi bond. In principle, there is no single step method to unambiguously obtain the most localized set of M.O.s in systems where several canonical structures are possible, just as no simple method exists for finding the most stable conformer of some large compound. However, the localized bonds generated will normally be quite acceptable for routine applications.

Localized orbitals are also known as Natural Bond Orbitals or NBO.