Spin‐projected EHF method. IV. Comparison of potential curves given by different one‐electron methods

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Abstract
Some aspects of the computer realization of the spin‐projected extended Hartree–Fock (EHF) method at the ab initio level are briefly discussed for the algorithm of solution developed in the previous papers of this series. Calculations have been performed for the BH molecule by using a small basis of contracted Gaussian lobes with the purpose of comparing the potential curves given by the different one‐electron methods RHF, UHF, UHF with subsequent spin projection, and EHF. It is concluded that the UHF and, in particular, the EHF methods give a qualitatively correct shape of the potential curve; the RHF method shows the known incorrect dissociation behavior while the potential curve obtained by subsequent spin projection of the UHF wave function exhibits spurious extrema at intermediate internuclear separations.