*
Journal of Chemical Physics 97, 7555-7559 (1992) *

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

^{a} Department of Chemistry, University of Warsaw, ul. Pasteura 1, 02-093 Warsaw, Poland

^{b} Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA

*
On the convergence of the symmetrized Rayleigh-Schrödinger perturbation theory for molecular interaction energies
*

** Abstract **

The generalized Heitler-London perturbation theory for molecular interaction
energies proposed recently by Tang and Toennies [J. Chem. Phys. 95, 5981 (1991)] is
proved to be equivalent to the symmetrized Rayleigh-Schrödinger perturbation expansion.
This theory is applied to the interaction of two
hydrogen atoms and is shown to reproduce the interaction energy
in the region of the van der Waals minimum to within about 1% already in the
third-order treatment. It is shown that the convergence radius of this theory is
the same as that of the polarization perturbation theory, i.e., is marginally
greater than unity at large interatomic distances R. This proximity
to unity results in a prohibitively slow high-order convergence of the expansion in the
region of the van der Waals minimum. Consequently, for the singlet state
at large R a small part of the exchange energy cannot be recovered in practice
by a direct term-by-term summation of the series. The perturbation
series resulting from the application of the theory to the antisymmetric triplet state
of H_{2} converges to an unphysical energy lying above
the energy of the triplet state. At large R the difference between the physical energy and the
unphysical limit of the series is very small and
can be neglected in practical applications of the theory.

Reprints are available on request. Send an e-mail to tatiana.korona@tiger.chem.uw.edu.pl

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