Inclusion of the (T) triples correction into the linear-r12 corrected coupled-cluster model CCSD(R12)

Heike Fliegl1, Christof Hättig2, Wim Klopper1,2
1Lehrstuhl für Theoretische Chemie, Institut für Physikalische Chemie, Universität Karlsruhe (TH), D-76128 Karlsruhe, Germany
2Institut für Nanotechnologie, Forschungszentrum Karlsruhe, P. O. Box 3640, D-76021 Karlsruhe, Germany

Intern. J. Quant. Chem., 106, 2306-2317 (2006).
Received 4 November 2005; accepted 2 Februar 2006
Puplished online 17 April 2006 in Wilez Interscience

The recently developed singles-and-cloubles linear-r12 corrected coupled-cluster model CCSD(R12) has been extended by inclusion of triples corrections in exactly the same manner as in the popular CCSD(T) model. The resulting model is denoted CCSD(T)(R12). An orthonormal auxiliary basis set is used for the resolution-of-the-identity approximation to calculate the three- and four-electron integrals needed in the linear-r12 Ansatz. CCSD(T)(R12) reaction energies are calculated for a test set of 15 chemical reactions involving 23 small molecules. The CCSD(T)(R12), CCSD(R12), and MP2-R12 results are compared with experimental data obtained by correcting experimental enthalpies of reaction for zero-point vibrational energies and finite temperature contributions. Conventional MP2, CCSD, and CCSD(T) results are presented for comparison. An estimate of the basis set limit is obtained by an aug-cc-pV(Q+d)Z/aug-cc-pV(5+d)Z CCSD(T) extrapolation for a subset of 12 reactions. All CCSD(T) results are compared with the extrapolated values, and the errors are analyzed for the CCSD(T) and CCSD(T)(R12) models in various basis sets. (C) 2006 Wiley Periodicals, Inc.

Correspondence to:W. Klopper;

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