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Deceptive convergence in møller-plesset perturbation energies

✍ Scribed by Peter M.W. Gill; Leo Radom

Publisher
Elsevier Science
Year
1986
Tongue
English
Weight
559 KB
Volume
132
Category
Article
ISSN
0009-2614

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✦ Synopsis

Msller-Plesset perturbation calculations (MPn) up to fiftieth order, within both the restricted (RHF) and unrestricted Hartree-Fock (UHF) frameworks, have been used to examine the He:+ ground-state potential curve. The bond lengths of the equilibrium and transition structures have been optimized at all orders of perturbation theory. It is found that RMPn describes the homolytic dissociation better than UMPn for all n > 2. This unexpected behaviour may be attributed to spin contamination in the UHF wavefunction. The UMPn barriers deceptively appear convergent for small n and the results may be indicative of dangers inherent generally in using the UMP approach with significantly spin-contaminated wavefunctions.

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