Filip Pawlowski
Department of Chemistry, University of Oslo,
P. O. Box 1033 Blindern, N-0315 Oslo, Norway
Poul Jørgensen
Department of Chemistry, Århus University,
DK-8000 Århus C, Denmark
Christof Hättig
Forschungszentrum Karlsruhe, Institute of Nanotechnology, P.O. Box 3640,
D-76021 Karlsruhe, Germany
Trygve Helgaker
Department of Chemistry, University of Oslo,
P. O. Box 1033 Blindern, N-0315 Oslo, Norway
Pawel Salek
Laboratory of Theoretical Chemistry, The Royal Institute of Technology,
SE-10691 Stockholm, Sweden
J. Chem. Phys. 124, 054322 (2006).
(Received 10 NOvember 2006; accepted 9 December 2005; published online 7 Februar 2006)
We present a detailed study of the effects of electron correlation on two-photon absorption calculated by coupled cluster quadratic response theory. The hierarchy of coupled cluster models CCS, CC2, CCSD, and CC3 has been used to investigate the effects of electron correlation on the two-photon absorption cross sections of formaldehyde (CH2O), diacetylene (C4H2), and water (H2O). In particular, the effects of triple excitations on two-photon transition cross sections are determined for the first time. In addition, we present a detailed comparison of the coupled cluster results with those obtained from Hartree-Fock and density-functional response theories. We have investigated the local-density approximation, the pure Becke-Lee-Yang-Parr (BLYP) functional, the hybrid Becke-3-parameter-Lee-Yang-Parr (B3LYP), and the Coulomb-attenuated B3LYP (CAM-B3LYP) functionals. Our results show that the CAM-B3LYP functional, when used in conjuction with a one-particle basis-set containing diffuse functions, has much promise; however, care must still be exercised for diffuse Rydberg-type states. (c) 2006 American Institute of Physics.
a) Author to whom correspondence should be addressed. Electronic mail: mjpaterson@chem.au.dk
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