## spin contamination

https://doi.org/10.1351/goldbook.ST07103
In unrestricted @H02747@–Fock method, the wavefunctions obtained are eigenfunctions of the Hamiltonian and the @ST07106@ $$S_{\text{z}}$$ operators, but not eigenfunctions of the $$S^{2}$$ operator. As a result, the wavefunctions of the doublet systems are spin-contaminated to some extent by admixtures of quartet, sextet, and higher spin states. The eigenvalues of the $$S^{2}$$ operator are given as a measure of the spin @C01295@.
Source:
PAC, 1999, 71, 1919. (Glossary of terms used in theoretical organic chemistry) on page 1962 [Terms] [Paper]