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Optimized accurate auxiliary basis sets for RI-MP2 and RI-CC2
calculations for the atoms Rb to Rn

Arnim Hellweg,^{a,b,*} Christof Hättig,^{b} Sebastian Höfener,^{c} Wim Klopper^{a,c}

^{a}Institut für Nanotechnologie, Forschungszentrum Karlsruhe,
D-76344 Karlsruhe, Germany

^{b}Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany

^{c}Lehrstuhl für Theoretische Chemie, Institut für Physikalische Chemie,
Universität Karlsruhe (TH), D-76128 Karlsruhe, Germany

*Theo. Chem. Acc.*, **117**, 587-597 (2007).

Received: 8 November 2006 / Accepted: 21 December 2006 / Published online: 23 January 2007

The introduction of the resolution-of-the-identity (RI) approximation
for electron repulsion integrals in quantum chemical calculations
requires in addition to the orbital basis so-called auxiliary or
fitting basis sets. We report here such auxiliary basis sets optimized
for second-order M phi ller-Plesset perturbation theory for the
recently published (Weigend and Ahlrichs Phys Chem Chem Phys, 2005, 7,
3297-3305) segmented contracted Gaussian basis sets of split,
triple-zeta and quadruple-zeta valence quality for the atoms Rb-Rn
(except lanthanides). These basis sets are designed for use in
connection with small-core effective core potentials including scalar
relativistic corrections. Hereby accurate resolution-of-the-identity
calculations with second-order M phi ller-Plesset perturbation theory
(MP2) and related methods can now be performed for molecules containing
elements from H to Rn. The error of the RI approximation has been
evaluated for a test set of 385 small and medium sized molecules, which
represent the common oxidation states of each element, and is compared
with the one-electron basis set error, estimated based on highly
accurate explicitly correlated MP2-R12 calculations. With the reported
auxiliary basis sets the RI error for MP2 correlation energies is
typically two orders of magnitude smaller than the one-electron basis
set error, independent on the position of the atoms in the periodic
table.

^{*}E-mail to: arnim.hellweg@theochem.rub.de

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