Weak antiferromagnetic coupling in molecular ring is predicted correctly by density functional theory plus Hubbard U

Abstract

We apply density functional theory with empirical Hubbard U parameter (DFT+U) to study Mn-based molecular magnets. Unlike most previous DFT+U studies, we calibrate U parameters for both metal and ligand atoms using five binuclear manganese complexes as the benchmarks. We note delocalization of the spin density onto acetate ligands due to pi-back bonding, inverting spin polarization of the acetate oxygen atoms relative to that predicted from superexchange mechanism. This inversion may affect the performance of the models that assume strict localization of the spins on magnetic centers for the complexes with bridging acetate ligands. Next, we apply DFT+U methodology to Mn(12) molecular wheel and find antiparallel spin alignment for the weakly interacting fragments Mn(6), in agreement with experimental observations. Using the optimized geometry of the ground spin state instead of less accurate experimental geometry was found to be crucial for this good agreement. The protocol tested in this study can be applied for the rational design of single molecule magnets for molecular spintronics and quantum computing applications.

Heisenberg coupling constant predicted for molecular magnets with pairwise spin-contamination correction

“…Hence, the phenomenon of spincontamination should be ignored. In fact, spin energy gap, predicted with BS DFT, can be found in a reasonable agreement with experimental values [34], [35]. Other researchers, however, recognize spin contamination as a problem affecting the energy.…”

Valence electronic structure of sublimated Fe4single-molecule magnets: an experimental and theoretical characterization

“…This type of comparison is not possible for Fe 4 (pta) 6 due to the lack of X-ray experimental structure. 51,52 In this framework, the inclusion of the U parameter on O 2p for a correct description of the electronic and, above all, the magnetic properties of the systems under study nds its justication in the necessity to accurately tune the amount of the delocalization of the electronic densities of the bridging ligands that are involved in the super-exchange paths. Indeed, the agreement comes from the ad hoc choice of the U values for the different elements made on the basis of the photoemission spectra (see ESI †).…”

Exchange coupling transformations in Cu (II) heterospin complexes of “breathing crystals” under structural phase transitions

“…19. Also, there are numerous evidences of the importance of the Hubbard term for oxygen [19][20][21] and nitrogen 22 atoms; the U value for oxygen ranging from 1.5 eV 22 to 8.5 eV. 19 C. Cao et al 20 found that increasing U for oxygen above 6 eV slightly effects on the magnetic coupling constant in single-molecule magnet Ni(hmp)(MeOH)Cl 4 .…”