Journal
MOLECULAR PHYSICS
Volume 109, Issue 22, Pages 2607-2623Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/00268976.2011.624129
Keywords
CCSD(T)-F12; explicit correlation; core-valence correlation; heavy elements
Funding
- US National Science Foundation [CHE-0723997]
- Deutsche Forschungsgemeinschaft (NSF-DFG)
- SimTech Cluster of Excellence at the University of Stuttgart
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A benchmark of explicitly correlated CCSD(T)-F12 methods for the dimers Ga-2, As-2, Br-2 and diatomic molecules AsN, BrO, HBr, GaF, GaCl, GaBr, AsF, AsCl, BrF, and BrCl is presented. Equilibrium distances, harmonic vibrational frequencies, and dissociation energies are compared with extensive conventional CCSD(T) calculations using a variety of orbital basis sets and different ansatze for the explicitly correlated wavefunctions. Correlation of the 3d electrons has a strong effect, in particular on the equilibrium distances, and it is shown that this can be recovered very efficiently by the explicit correlation treatment. It is found that CCSD(T)-F12 calculations with new F12-specific cc-pVnZ-F12 basis sets give comparable accuracy to standard CCSD(T) calculations with very much larger aug-cc-pwCV(n+2)Z basis sets. The effects of higher order valence electron correlation (up to CCSDTQP) are also investigated in conventional calculations and are found to be significant in some cases.
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