MCDHF/DC+B-adjusted pseudopotentials for lanthanides and quantum chemical investigations of lanthanide compounds with unusual electronic structure

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Relativistic energy-consistent small-core (28 core electrons) ab initio pseudopotentials will be derived for the lanthanide elements La (Z=57) to Lu (Z=71) from multi-configuration Dirac-Hartree-Fock reference data based on the self-consistent treatment of the finite nucleus Dirac-Coulomb Hamiltonian and a perturbative treatment of the low-frequency limit of the Breit interaction. The goal is to reach an accuracy of better than 0.01 eV for the total energies of various configurations ranging from the neutral atom to highly charged ions with holes in the semi-core orbitals 4s, 4p, 4d, 5s and 5p. Generally contracted atomic natural orbital basis sets, for one- and two-component calculations, with up to quadruple-zeta quality will be derived. The pseudopotentials will be calibrated in atomic as well as molecular (e.g., selected monohydrides, monoxides, and monofluorides) correlated calculations against corresponding all-electron ab initio reference data as well as against experimental data if available.The pseudopotentials will be applied to study lanthanide systems with unusual bonding situations, e.g., the sandwich compounds cerium bis(pentalene), cerium bis(phthalocyanine) and cerium tris(cyclopentadienly) cation and diatomic ytterbium monoxide. In the first case the oxidation state of Ce will be investigated. It will be checked if the system has a similar Ce(3+) Kondo-type open-shell singulet ground state as cerium bis(cyclooctatetraene), cerocene.In the second case it will be examinated if the configurational mixing between Yb subconfigurations with 13 and 14 electrons in the 4f shell leads to the unusual spectroscopic constants of the 0+ ground state, exhibiting a bond length typical for Yb(2+) 4f13 6s1 O(2-) and a vibrational frequency typical for Yb(2+) 4f14 O(2-).