Xiaoyan Cao-Dolg – Projects
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 f^{n} d^{1} s^{2} and f^{n+1} s^{2} 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 (La_{2}, Ce_{2}, Eu_{2}, Gd_{2}, Yb_{2}, Lu_{2}) was investigated in large-scale correlated electronic structure calculations. It was concluded that, e.g., the ground state configurations of La_{2} and Lu_{2} differ (mainly) due to an increase of relativistic effects and (partially) shell structure effects. The vibrational frequency of the La_{2} system is most likely affected by the rare gas matrix much more than the one of the Lu_{2} system, thus explaining remaining differences with recent experimental data. Gd_{2} 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-Tex^{2+}, 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):
- Lanthanide ANO generalized contracted basis sets
- Actinide ANO generalized contracted basis sets
- Lanthanide segmented contracted basis sets
- Actinide segmented contracted basis set