*
Molecular Physics 100 , 1723-1734 (2002)*

Tatiana Korona, Robert Moszynski, and Bogumil Jeziorski

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

*
Electrostatic interactions between molecules
from relaxed one-electron density matrices of the coupled cluster singles
and doubles model*
^{ a}

** Abstract **

The influence of the electron correlation on
the electrostatic interaction between closed-shell molecules
is studied using the relaxed electron densities of
the coupled cluster singles and doubles model (CCSD).
The corresponding CCSD one-electron density matrices are efficiently
computed without full four-index transformation by employing the generalized
exchange and Coulomb operator technique.
Using several representative van der Waals and hydrogen-bonded
complexes we found that in most cases
the convergence of the Møller-Plesset expansion of the
electrostatic energy, restricted to single, double and
quadruple excitations, is quite satisfactory and
the fourth-order triple excitation term
is more important than the sum of the fifth- and higher-order contributions
from the CCSD theory. The importance of the CCSD correlation
correction to the electrostatic energy was gauged by comparison
of the total interaction energy computed by
the symmetry-adapted perturbation theory (SAPT) and by the
supermolecular CCSD(T) approach (coupled cluster singles and doubles
model with a noniterative inclusion of triple excitations).
Except for the CO and N_{2} dimers
very good agreement between the two sets of results is observed.
For the difficult case of the CO dimer the difference between the
SAPT and CCSD(T) results can be explained by
the truncation of the SAPT expansion for the dispersion energy
at the second order in the intramonomer correlation operator.

^{ a}
Dedicated to Professor
E. R. Davidson on the occasion of his 65th birthday

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

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