Optimized partitioning in perturbation theory: Comparison to related approaches

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Abstract

A generalized Epstein-Nesbet type perturbation theory is introduced by a unique, "optimal" determination of level shift parameters. As a result, a new partitioning emerges in which third order energies are identically zero, most fifth order terms also vanish, and low (2nd, 4th) order corrections are quite accurate. Moreover, the results are invariant to unitary transformations within the zero order excited states. Applying the new partitioning to many-body perturbation theory, the perturbed energies exhibit appealing features: (i) they become orbital invariant if all level shifts are optimized in an excitation subspace; and (ii) meet the size-consistency requirement if no artificial truncations in the excitation space is used. As to the numerical results, low order corrections do better than those of Møller-Plesset partitioning. At the second order, if the single determinantal Hartree-Fock reference state is used, the CEPA-0 (=LCCD) energies are recovered. Higher order corrections provide a systematic way of improving this scheme, numerical studies showing favorable convergence properties. The theory is tested on the anharmonic linear oscillator and on the electron correlation energies of some selected small molecules.

Original languageEnglish
Pages (from-to)4438-4446
Number of pages9
JournalThe Journal of Chemical Physics
Volume112
Issue number10
Publication statusPublished - Mar 8 2000

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Electron correlations
Excited states
perturbation theory
Molecules
excitation
energy
shift
oscillators
orbitals
requirements
approximation
molecules
electrons

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Optimized partitioning in perturbation theory : Comparison to related approaches. / Surján, P.; Szabados, A.

In: The Journal of Chemical Physics, Vol. 112, No. 10, 08.03.2000, p. 4438-4446.

Research output: Contribution to journalArticle

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