Annihilated unrestricted Hartree-Fock method

A third alternative is to use projection methods during the determination of the wave function. Annihilated unrestricted Hartree-Fock (AUHF) uses a projector or annihilator to remove spin contamination from the density used to construct the unrestricted a and P Fock matrices. The spin constrained Hartree-Fock method (SUHF) adds A. 

Theoretical Results. To solve the open-shell problem, various MO methods have been applied and, in some cases, compared with each other. Most commonly, the restricted Hartree-Fock formalism for the open-shell case (RHF) [15] and the unrestricted Hartree-Fock formalism before (UHF) [16] and after single spin annihilation (UHFASA) [17] have been used besides other methods, see [18 to 21] and footnote of Table 6, p. 234. 

---