On The Density Functional Theory Treatment of Lanthanide Coordination Compounds: A Comparative Study in a Series of Cu-Ln (Ln = Gd, Tb, Lu) Binuclear Complexes.

The nontrivial aspects of electron structure in lanthanide complexes, considering ligand field (LF) and exchange coupling effects, have been investigated by means of density functional theory (DFT) calculations, taking as a prototypic case study a series of binuclear complexes [LCu(O2COMe)Ln(thd)2], where L2- = N,N'-2,2-dimethyl-propylene-di(3-methoxy-salicylidene-iminato) and Ln = Tb, Lu, and Gd. Particular attention has been devoted to the Cu-Tb complex, which shows a quasi-degenerate nonrelativistic ground state. Challenging the limits of density functional theory (DFT), we devised a practical route to obtain different convergent solutions, permuting the starting guess orbitals in a manner resembling the run of the ß electron formally originating from the f8 configuration of the Tb(III) over seven molecular orbitals (MOs) with predominant f-type character. Although the obtained states cannot be claimed as the DFT computed split of the 7F multiplet, the results are yet interesting numeric experiments, relevant for the ligand field effects. We also performed broken symmetry (BS) DFT estimation of exchange coupling in the Cu-Gd system, using different settings, with Gaussian-type and plane-wave bases, finding a good match with the coupling parameter from experimental data. We also caught BS-type states for each of the mentioned series of different states emulated for the Cu-Tb complex, finding almost equal exchange coupling parameters throughout the seven LF-like configurations, the magnitude of the J parameter being comparable with those of the Cu-Gd system.

Magnetic Structures of Heterometallic M(II)-M(III) Formate Compounds.

A study of the magnetic structure of the [NH2(CH3)2]n[FeIIIMII(HCOO)6]n niccolite-like compounds, with MII = CoII (2) and MnII (3) ions, has been carried out using neutron diffraction and compared with the previously reported FeII-containing compound (1). The inclusion of two different metallic atoms into the niccolite-like structure framework leads to the formation of isostructural compounds with very different magnetic behaviors due to the compensation or not of the different spins involved in each lattice. Below TN, the magnetic order in these compounds varies from ferrimagnetic behavior for 1 and 2 to an antiferromagnetic behavior with a weak spin canting for 3. Structure refinements of 2 and 3 at low temperature (45 K) have been carried out combining synchrotron X-ray and high-resolution neutron diffraction in a multipattern approach. The magnetic structures have been determined from the difference patterns between the neutron data in the paramagnetic and the magnetically ordered regions. These difference patterns have been analyzed using a simulated annealing protocol and symmetry analysis techniques. The obtained magnetic structures have been further rationalized by means of ab initio DFT calculations. The direction of the magnetic moment of each compound has been determined. The easy axis of the MII for compound 1 (FeII) is along the c axis; for compound 2 (CoII), the moments are mainly within the ab plane; finally, for compound 3 (MnII), the calculations show that the moments have components both in the ab plane and along the c axis.

Ferromagnetism and orbital order in a topological ferroelectric.

We explore via density functional calculations the magnetic doping of a topological ferroelectric as an unconventional route to multiferroicity. Vanadium doping of the layered perovskite La(2)Ti(2)O(7) largely preserves electric polarization and produces robust ferromagnetic order and, hence, proper multiferroicity. The marked tendency of dopants to cluster into chains results in an insulating character at generic doping. Ferromagnetism stems from the symmetry breaking of the multiorbital V system via an unusual "antiferro"-orbital order, and from the host's low-symmetry layered structure.