Abstract
To examine the effects of including quadruple excitations in the electron correlation treatment when computing the binding energy of van der Waals dimers, we have calculated MP2, CCSD, CCSD(T), and CCSD(TQ) interaction energies for several van der Waals complexes ranging from helium dimer to furan dimer. Through comparison of CCSD(TQ) and CCSD(T) binding energies the first direct assessment of the effects of quadruple excitations on π⋯π interactions is presented. The influence of triple excitations is assessed not only in the conventional manner that permeates the literature (comparison of CCSD(T) and MP2 interaction energies) but also via comparison of CCSD(T) and CCSD data. In systems exhibiting significant electron delocalization, it is well-known that triples contributions to binding energy are quite large (on the order of l kcal mol-1). In these cases, quadruple excitations are nonnegligible and tend to be an order of magnitude smaller than the correction to the binding energy from triple excitations (on the order of 0.1 kcal mol-1). The largest quadruples correction observed was +0.2 kcal mol-1 for the furan dimer.
Recommended Citation
B. W. Hopkins and G. S. Tschumper, "Ab Initio Studies of Π⋯π Interactions: The Effects of Quadruple Excitations," Journal of Physical Chemistry A, vol. 108, no. 15, pp. 2941 - 2948, American Chemical Society, Apr 2004.
The definitive version is available at https://doi.org/10.1021/jp0369084
Department(s)
Chemistry
International Standard Serial Number (ISSN)
1089-5639
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2024 American Chemical Society, All rights reserved.
Publication Date
15 Apr 2004
