SPIN-PROJECTED EXTENDED HARTREE-FOCK USING A VALENCE-BOND APPROACH

We describe spin-projected Extended Hartree-Fock calculations, perform ed with a Valence Bond Self-Consistent Field program. Potential energy curves are given for BH, BeH, and N2. For BH the EHF function ranks w ell with the corresponding Spin-coupled and full CI wave functions. Fo r BeH, the EHF function introduces spin contamination in the separated Be atom due to the rigidity of the wave function. This results in an inferior potential energy curve compared to Spin-coupled and full CI. The triple bond breaking in N2 is again nicely described by EHF. The E xtended Hartree-Fock method as suggested by Lowdin can be a feasible t ool in describing bond breaking.