Joint research project

Density Functional Theory calculations for lanthanide complexes.

Project leaders
Alessandro Stroppa, Fanica Cimpoesu
Agreement
ROMANIA - RA - The Romanian Academy
Call
CNR/RA 2014-2016
Department
Physical sciences and technologies of matter
Thematic area
Physical sciences and technologies of matter
Status of the project
New

Research proposal

The project deals with theoretical calculations of d and f complexes based on multiconfiguration methods and density functional theory (DFT).The involved groups show complementary expertise: the director of the Italian team has a long standing and advanced experience with electronic structure calculations for extended solid state systems [Nat. Mat. 2010, 9, 741; Angew Chem Int Ed.2011, 50, 5847; Adv. Mat. 2013 25, 2284]; the romanian team has a firm experience with pioneering contribution in the field of molecular magnetism. [Inorg. Chem. 2012, 51, 40; Inorg. Chem. 2012, 51, 11279; Dalton Trans., in press]. In particular, they performed the first ab initio calculation on lanthanide complexes, [JACS, 2004, 126, 3321] and significantly contributed to the description of the complex issue of magnetic anisotropy, offering clear methodologies, with very intuitive graphic representations (polar maps of state-specific magnetization functions) revealing the orientation and the extension of magnetization axes. [JACS, 2006, 128, 9008; Inorg. Chem. 2011, 50, 9678]

Research goals

The field of molecular magnetism in the last two decades has gradually evolved from the search for ever larger spin-state complexes as potential Single Molecule Magnets (SMMs) to the current trend of small molecules with modest ground-state spin values but strong magnetic anisotropy properties. As a matter of fact, it has been realized that for larger size complexes, the key property for the magnetic memory effect - the easy-axis anisotropy - is reduced compared to smaller size molecules. Therefore, there is nowadays an increasing focus in the family of lanthanide-based SMMs [Inorg. Chem. 2012, 51, 12055].
However, the quantum chemistry of lanthanides is more complicated than those of d-type complexes, due to the non-aufbau configuration and weakly interacting features of the f shell. We devised previously a strategy for the multiconfigurational treatment via Complete Active Space Consistent Field (CASSCF) using wavefunctions assembled from fragments (the free lanthanide ions plus the rest of the complex). Initially, it was claimed that the DFT methods cannot be used for f complexes because of their limitation to single determinant wavefunctions. However, recently, molecular calculations of several Cu-Gd complexes were presented [Dalton Trans. 2011, 40, 10897] proving that at least for Gd(III), where the groundstate is non- degenerate, the unrestricted DFT can be used. We considered also the case of terbium complexes, in order to assess the applicability of DFT to multiplet problems and to theligand field (LF) effects. Using codes for molecular quantum chemistry (Gamess, Gaussian) and a Cu-Tb complex proved with Single Molecule Magnet (SMM) behaviour [Inorg. Chem. 2006, 45, 5] as case study, we found seven different DFT solutions resembling the LF split of the 7F term of Tb(III) ion, using the strategy of fragment-assembled starting functions and the permutation of orbitals, as initialization for the different configurations. The purpose of the present project is a comparative study the electronic structure of several 4f complexes based on different methodologies, namely based on plane wave basis sets (VASP) or Gaussian basis sets (Gamess, Gaussian) to clearly assess the advantages and limitations of each approach with respect to select case studies. Furthermore, we will address the study of magnetic anisotropy in these complexes. The magnetic anisotropy is a running paradigm of the nowadays molecular magnetism, stirring interest both from academic point of view, since it has intricate mechanism, and also for application purposes, its understanding serving to design systems behaving as magnets at molecular and nano-scale levels.

Last update: 07/10/2022