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

Abstract

AbstractsSome 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.On discute britvement quelques aspects des calculs pratiques au niveau ab initio selon la mtthode Hartree-Fock itendue (EHF) par projection de spin, dans la forme dCveloppCe dans d'autres articles de cette strie. Des calculs ont CtC faits pour la molCcule BH avec un petit jeu de base de lobes gaussiens contract&. Le but de ces calculs est de comparer les courbes de potentiel obtenues par des mtthodes differentes: RHF, UHF, UHF suivie de projection par rapport au spin et EHF. I1 en decoule, que UHF et surtout EHF donnent une forme qualitativement correcte de la courbe de potentiel; la mtthode RHF prisente le comportement de dissociation incorrect bien connu, tandis que la courbe obtenue par UHF suivie de projection prisente des points extrimes faux k des separations internuclkaires intermtdiaires.Einige Aspekte der Computer-Durchfiihrung am ab-initio-Niveau der Spinprojizierten verallgemeinerten Hartree-Fock-Methode (EHF) in der in friiheren Artikeln dieser Reihe entwickelten Form werden kurz diskutiert. Berechnungen sind fur das BH-Molekiil mit einem kleinen Basissatz von kontrahierten Gaussloben ausgefiihrt worden, um die mit verschiedenen Methoden (RHF, UHF, UHF mit anschliessender Spinprojektion, EHF) erhaltenen Potentialkurven zu vergleichen. Es zeigt sich, dass UHF und besonders EHF eine qualitativ korrekte Form der Potentialkurve geben. Die RHF-Methode erweist das wohlbekannte unrichtige Dissoziationsverhalten, wahrend die von UHF mit anschliessender Spinprojektion erhaltene Kurve unechte Extrempunkte an Zwischenkernabstanden aufweist.

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