SPIN CONTAMINATION IN DENSITY-FUNCTIONAL THEORY

Local density functional calculations on a series of small, neutral ra dicals demonstrate that the unrestricted Kohn-Sham wavefunction is muc h less contaminated by higher spin states than its unrestricted Hartre e-Fock counterpart, even for radicals which exhibit major contaminatio n in their standard UHF wavefunction. A study of the dissociation curv es for the OH and CN radicals shows that the UKS wavefunction remains essentially spin pure out to about 1.5 rimes the equilibrium bond leng th. Some general observations regarding spin contamination in unrestri cted SCF wavefunctions are presented.