DFT calculations of molecular magnetic properties of coordination compounds

An overview of density functional theory (DFT) based techniques for the calculation of the magnetic properties of molecular and supramolecular assemblies is presented. Three different approaches to compute the exchange coupling constant (J(ex)) are reviewed, i.e. the broken symmetry (BS) technique, the single determinant (SD) approach, and the spin projection method. The first one (BS), developed by Noodleman, is undoubtedly most commonly applied, e.g. to clusters containing several paramagnetic metal centres or to paramagnetic organic radical species. The second approach (SE)) was originally developed to compute the electronic spectra of transition metal complexes, but was more recently applied to the computation of spin manifold of molecular magnets. The last method, developed by Ovchinnikov and Labanowsky, is mainly an extension of the Hartree-Fock (HF) concept of spin decontamination to DFT. The performance of the three methods has been evaluated for model systems (HHeH, [Cu2Cl6](2-)) and for more complex molecules (Ti(CatNSQ)(2) and Sn(CatNSQ)(2), Bis-verdazyl diradical (BVD), [Fe-2(OH)(3)(tmtacn)(2)](2+) and [[Cu3O2L3](3+), L = N-Permethylated (1R, 2R)-cyclohexanediamine]. A comparison of these results with experimental values and with post-H F results if available is presented as well. In the case of the last two complexes, i.e. mixed valence systems, computation of the vibronic potential energy surfaces is also briefly discussed. (C) 2003 Elsevier Science B.V. All rights reserved.