Optimized Basis Sets for Lanthanide and Actinide Systems and their
Application in Quantum Chemical Calculations
Xiaoyan Cao, Michael Dolg
Institute for Theoretical Chemistry, University of Cologne
contact: x.cao@uni-koeln.de
Ab initio calculations of the electronic structure of lanthanide and actinide
elements and their molecules are very demanding due to the large relativistic
and electron correlation effects. The ab initio energy-consistent pseudopotential
approach proved to be a reliable approximate relativistic scheme for calculations
of the valence electron structure of lanthanide and actinide systems when
a small core is used. However, the previously published pseudopotentials
for lanthanides (Dolg, Stoll, Preuss, J. Chem. Phys. 90 (1989) 1730 - 1734)
and actinides (Küchle, Dolg, Stoll, Preuss, J. Chem. Phys. 100 (1994)
7535 - 7542) were not supplemented by systematic and reliable basis sets.
Therefore new polarized valence basis sets of roughly quadruple-zeta quality
have been generated for both the 4f and 5f series. An atomic natural orbital
based generalized contraction scheme was applied, which allows to reduce
the basis set size to triple- or double-zeta quality by omitting the outermost
contractions corresponding to the least occupied atomic natural orbitals.
The contractions coefficients were usually optimized for the fn
d1 s2 and fn+1 s2 configurations
simultaneously by averaging the corresponding density matrices. As an alternative
segmented contracted basis sets were also derived. Both sets were sucessfully
tested in atomic and molecular calibration calculations (e.g. for some monohydrides,
monoxides and monofluorides) and are available e.g. through the Stuttgart Pseudopotential
and Valence Basis Sets www-page (cf. also the download area below !).
As an application the electronic structure of selected lanthanide dimers
(La2, Ce2, Eu2, Gd2, Yb2,
Lu2) was investigated in large-scale correlated electronic structure
calculations. It was concluded that, e.g., the ground state configurations
of La2 and Lu2 differ (mainly) due to an increase of
relativistic effects and (partially) shell structure effects. The vibrational
frequency of the La2 system is most likely affected by the rare
gas matrix much more than the one of the Lu2 system, thus explaining
remaining differences with recent experimental data. Gd2 is confirmed
to have 18 unpaired electrons in the ground state, 14 of them in the two
4f shells.
The higher lanthanide and actinide ionization potentials exhibit very large
differential electron correlation effects, since the f occupation number
of the involved electronic states changes. In order to come to reliable estimates
for the higher ionization potentials, we performed at the CASSCF/ACPF and
partially at the CCSD(T) level (including spin-orbit correlations) basis
set extrapolation studies using uncontracted valence basis sets with up to
i-type functions. The results are in good agreement with the experimentally
better known values for the lanthanides and provide (in our opinion) the
best and most complete theoretical set of values for the actinides. Similar
techniques have been recently used to calculate the electron affinity of
the Ce atom. Here we obtained excellent agreement with all-electron ab initio
calculations as well as earlier experimental results, whereas the most recent
experiment was interpreted to lead to a substantially higher value.
Finally, using large-core (4f-in-core) pseudopotentials we investigated selected
lanthanide(III)texaphyrin complexes, which are important for cancer theraphy.
This work is currently continued to evaluate the relevant part of the electronic
excitation spectra in a realistic solvent model.
Publications:
- Valence basis sets for relativistic energy-consistent small-core
lanthanide pseudopotentials. X. Cao, M. Dolg, J. Chem. Phys. 115 (2001) 7348
- 7355.
- Basis set limit extrapolation of ACPF and CCSD(T) results
for the third and fourth lanthanide ionization potentials. X. Cao, M. Dolg,
Chem. Phys. Lett. 349 (2001) 489 - 495.
- Molecular structure of diatomic lanthanide compounds. X.
Cao, W. Liu, M. Dolg, Science in China B 31 (2001) 481 - 486; engl. 45 (2002)
91 - 96.
- Segmented contraction scheme for small-core lanthanide pseudopotential
basis sets. X. Cao, M. Dolg, J. Molec. Struct. (Theochem) 581 (2002) 139
- 147.
- Pseudopotential study of lanthanum and lutetium dimers. X.
Cao, M. Dolg, Theor. Chem. Acc. 108 (2002) 143 - 149.
- Valence basis sets for relativistic energy-consistent small-core
actinide pseudopotentials. X. Cao, M. Dolg, H. Stoll, J. Chem. Phys. 118
(2003) 487 - 496.
- Theoretical prediction of the second to fourth actinide ionization
potentials. X. Cao, M. Dolg, Mol. Phys. 101 (2003) 961 - 969.
- Electronic structure of lanthanide dimers. X. Cao, M. Dolg,
Mol. Phys. 101 (2003) 1967 - 1976.
- New basis sets for lanthanide and actinide small-core pseudopotentials.
X. Cao, J. Chinese Chem. Soc. 50(3B) (2003) 665 - 676.
- Density functional studies on lanthanide (III) texaphyrins
(Ln-Tex2+, Ln = La, Gd, Lu). Structure, stability and electronic
excitation spectrum. X. Cao, M. Dolg, Mol. Phys. 101 (2003) 2427 - 2435.
- The relativistic energy-consistent ab initio pseudopotential
approach and its application to lanthanide and actinide compounds. M. Dolg,
X. Cao, in: Recent Advances in Computational Chemistry, Vol. 6, eds.
K. Hirao, Y. Ishikawa, World Scientific, New Jersey (2004), in press.
- Segmented contraction scheme for small-core actinide pseudopotential
basis sets. X. Cao, M. Dolg, J. Molec. Struct. (Theochem) 673 (2004) 203
- 209.
- Electron affinity of Ce and electronic states of Ce-1.
X. Cao, M. Dolg, Phys. Rev. A, in press..
Pseudopotentials and basis sets to download (ASCII):
Posters to download (pdf):