Atomization Energies from Coupled-Cluster Calculations Augmented with Explicitly-Correlated Perturbation Theory
Wim Klopper,a Branko Ruscic,b David P. Tew,a Florian A. Bischoff,a and Sandra Wolfseggera
a Lehrstuhl f�r Theoretische Chemie, Institut f�r Physikalische Chemie, Universit�t Karlsruhe (TH), D-76128 Karlsruhe, Germany
b Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
Chem. Phys.
356(1-3), 14-24 (2009)
The atomization energies of the 105 molecules in the test set of Bakowies
[D. Bakowies, J. Chem. Phys. 127 (2007) 084105]
have been computed with an estimated standard deviation (from the values compiled in
the Active Thermochemical Tables) of �0.1 kJ/mol per valence electron in the molecule.
Equilibrium geometries and harmonic vibrational frequencies were calculated at the all-electron
CCSD(T)/cc-pCVTZ level, that is, at the level of coupled-cluster theory with singles, doubles
and non-iterative triples in a correlation-consistent polarized core�valence triple-zeta basis.
Single-point energy calculations were performed at the all-electron CCSD(T) level in a
correlation-consistent polarized core�valence quadruple-zeta basis (cc-pCVQZ), and several
corrections were added: (i) a correction for the basis-set truncation error, obtained from
second-order perturbation theory using Slater-type geminals (MP2-F12 theory),
(ii) a correction for the effect of anharmonicity on the zero-point vibrational energy,
(iii) a relativistic correction, (iv) a correction for the difference between the full CCSDT model
(coupled-cluster theory with singles, doubles and triples) and the CCSD(T) approximation, and
(v) a correction for connected quadruple excitations obtained from CCSDT(Q) calculations.
The correction for the basis-set truncation error was obtained from MP2-F12 calculations by scaling
the MP2 basis-set truncation error by an empirically optimized �interference factor� of
fint = 0.78.
The reference values from the Active Thermochemical Tables for 73 molecules in the test set,
the equilibrium geometries, the harmonic vibrational frequencies, and all of the energy corrections
represent valuable data for performance assessments of additivity schemes that will be developed
in the future, in which the basis-set truncation error will be calculated at the level of
coupled-cluster theory using Slater-type geminals (CC-F12 theory). Such a scheme will be free
of empirical corrections and scaling factors.