Tatiana Cwiok^{a}, Bogumil Jeziorski^{b,a}, Wlodzimierz
Kolos^{a}, Robert Moszynski^{b,a}, and Krzysztof Szalewicz^{c}

^{a} Department of Chemistry, University of Warsaw, Pasteura
1, 02093 Warsaw, Poland
^{b} Institute of Theoretical Chemistry, University of Nijmegen,
Toernooiveld, 6525 ED Nijmegen, Netherlands
^{c} Department of Physics and Astronomy, University of Delaware,
Newark, DE 19716, USA

*Symmetry-adapted perturbation theory of potential-energy
surfaces for weakly bound molecular complexes*

**Abstract**

The symmetry-adapted perturbation theory (SAPT) expansions for the intermolecular
interaction energies can provide potential energy surfaces for weakly bound
complexes such as van der Waals molecules or systems forming hydrogen bonds.
The convergence properties of SAPT expansions are discussed. New results
are presented for the Hirschfelder-Silbey (HS) method applied through high
order to the interaction of two ground-state hydrogen atoms. As has been
shown for the case of the interaction of a hydrogen atom with a proton,
the HS theory converges very well. At low order this theory provides results
very close to those of the symmetrized Rayleigh-Schrödinger (SRS)
approach. In particular, the differences are negligible at the second order,
i.e. at the level which can be practically applied to larger systems. Our
results indicate that these two SAPT methods properly account for the electron
exchange effects. The singlet-triplet splitting at the van der Waals minimum,
obtained from the SRS exchange energy through second order, is considerably
more accurate than that obtained from the asymptotically exact Herring
and Flicker formula. The many-body version of the SRS theory is briefly
discussed and the results of its applications to several many-electron
systems (He_{2}, He-K^{+}, Ar-H_{2}, He-HF and
Ar-HF) are presented. In all cases a very good agreement, generally within
a few per cent or less, between theoretical and experimental binding energies
was found.

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