Molecular equilibrium geometries based on coupled-cluster calculations including quadruple excitations

Miriam Heckert, Mihály Kállay, Jürgen Gauss

Research output: Contribution to journalArticle

123 Citations (Scopus)

Abstract

Using analytic gradient techniques and an additivity scheme for the various electron correlation contributions, i.e. core-correlation, contribution due to full treatment of triple excitations and contributions due to quadruple excitations calculated with different basis sets, the accuracy of computed geometrical parameters are analysed in comparison with experiment. For a test set of 12 closed-shell and 5 open-shell molecules, it is found that inclusion of quadruple excitations is essential to reach agreement with experiment. The mean error of 0.002 pm and the standard deviation of 0.040 pm of the present CCSD(T)/cc-pV6Z + core(CCSD(T)/cc-pCVQZ) + T/cc-pVTZ + Q/cc-pVDZ results for the closed-shell systems underline the importance of quadruple excitations, in particular, as corresponding calculations without quadruple excitations exhibit significantly larger error. Quadruples contributions for multiply bonded systems as well as the challenging F2 molecule are as large as 0.1 to 0.3 pm, while for single bonds the effects are typically significantly smaller than 0.1 pm.

Original languageEnglish
Pages (from-to)2109-2115
Number of pages7
JournalMolecular Physics
Volume103
Issue number15-16
DOIs
Publication statusPublished - Aug 10 2005

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Electrons
Electron correlations
Molecules
Geometry
geometry
excitation
Experiments
molecules
standard deviation
single bond
inclusions
gradients
electrons

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Molecular equilibrium geometries based on coupled-cluster calculations including quadruple excitations. / Heckert, Miriam; Kállay, Mihály; Gauss, Jürgen.

In: Molecular Physics, Vol. 103, No. 15-16, 10.08.2005, p. 2109-2115.

Research output: Contribution to journalArticle

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