Yu. V. Stulov.
ABSTRACT
The main problems appearing in the quantum-chemical modeling of complex lanthanide (Ln) ions are considered. The principal difficulty is the presence of an open 4f shell in the Ln ions, which leads to a large number of quasi-revealed electronic states that cannot be correctly described by single-configuration methods. Various approaches to the quantum chemical modeling of systems containing Ln complexes are analyzed. We considered the basis sets in which 4f electrons are taken into account explicitly (4f-in-valence) and the bases in which 4f electrons are taken into account in the effective core potential (the core potential is determined by a number of electrons located near the nucleus and not involved in the formation of chemical bonds, 4f-in-core). It is shown that quantum-chemical calculations by the Hartree-Fock methods and the density functional theory can lead both to the incorrect distribution of the electron density of the complex, which is typical for the 4f-in-valence bases, and to the incorrect description of the coordination number of the complex ion when using the 4f-in-core basis sets. The incorrect reproduction of the structure of the complexes is apparently related to the inability to take into account the interaction of the 4f orbitals with the ligand field. Nevertheless, we proposed an approach that consists in using the 4f-in-core basis for the samarium atom together with locking the structure of the complex. This makes it possible to obtain a correct simulation of the composition of the first coordination sphere of the complexes and the undistorted electronic structure of the complex particle. A good agreement between the results of quantum-chemical modeling and experimental data is observed. It is shown that the use of 4f-in-core bases also leads to a significant reduction in the amount of machine time required, which makes it possible to use these bases in routine calculations. This approach can be extended for other Ln-containing model systems as well.
KEYWORDS
Quantum-chemical calculations, Hartree-Fock method, Density Functional Theory, Lanthanide complexes, Samarium, 4f-in-core.
DOI: 10.31857/S0235010622060123