Tatiana Korona, Robert Moszynski, and Bogumil Jeziorski

Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland

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Convergence of symmetry-adapted perturbation theory expansions for pairwise nonadditive interatomic interactions
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**Abstract**

Convergence properties of symmetry-adapted perturbation expansions for nonadditive interactions
are tested by performing high-order calculations for three
spin-aligned hydrogen atoms. It is shown that the strong
symmetry forcing characteristic of the Hirschfelder-Silbey theory leads to a rapidly convergent
perturbation series. The symmetrized Rayleigh-Schrödinger perturbation theory employing a weak
symmetry forcing is shown to provide in low orders accurate approximations to the
nonadditive part of the interaction energy. In very high orders the convergence of
this perturbation expansion becomes very slow, and the series converges to
an unphysical limit, very close to the exact interaction energy. The nonadditive part of the
interaction energy for the lowest quartet state of
H_{3} is interpreted in terms of the first-order exchange, induction, exchange-induction,
exchange-dispersion, induction-dispersion, and dispersion contributions. It is shown
that even for such a simple trimer the correct description of these components
is necessary to obtain quantitative agreement with variational full configuration interaction results.

Back to the publication list of Tatiana KoronaTatiana Korona 2003-01-17