MODELLING OF MOLECULAR SPIN CLUSTERS
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Valerio Bellini
Density-functional simulations of gas-phase magnetic molecules and their supramolecular assembly
Electronic and spin degrees of freedom are usually decoupled in magnetic molecules, such that the magnetic properties could be successfully simulated by (only) considering spin Hamiltonians with different isotropic (Heisenberg exchange) and anisotropic (single-ion, dipolar, anisotropic exchange) interactions. Such quantities, together with information on the energies and orbital character of the molecular wave functions could be extracted from first-principle calculations (with DFT or more refined ab-initio multi-determinantal methods). Monomeric or dimeric supramolecular complexes have been addresses. We have so far concentrated on the family of antiferromagnetic molecular Cr7M rings (see Figure 2). The propagation of the spin information between two Cr7Ni rings through heteroaromatic bridges, e.g. bipyrazine, bipyridine, etc…, has been also simulated (see Figure 3). Further properties have been studied, such as the simulation of hyperfine fields at nuclei, responsible of the part of the decoherence of the quantum spins in these molecular systems.
DFT codes relying on standard (augmented) plane-waves, e.g. Wien2K, and, recently, Gaussians based basis sets, i.e. NWChem, have been used for the simulations.
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Fig 1. Iso-surface plots of the electron spin density in Cr7M, M=Ni, Mn, Fe and Cu rings of the “green ”derivative in the AFM state (isovalues of ± 0.01 electrons / a.u. have been used); different colors are relative to positive (blue) and negative (yellow) values of the spin density, referred to the total spin of the molecule in the AFM state, which is set to positive.
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Fig 2. The molecular structures of [{Cr7NiF3(Etglu)(O2CtBu)16}2(L)], with L= pyrazine, bidimethylpyrazolyl, 4,4'-bipyridyl, trans-1,2-bipyridylethene and bipyridyltetrazine. The atoms of the linkers (N, blue; C, gray; H, white) and the metal ions in the rings (Ni, yellow; Cr, green) have been highlighted; the inter-rings through-space Ni-Ni distances (d) are also given for each dimer
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Publications
A Density-Functional Study of Heterometallic Cr-Based Molecular Rings.
V. Bellini and M. Affronte
J. Phys. Chem. B. 114, 14797 (2010).
Spin entanglement in supramolecular structures.
F. Troiani, V. Bellini, A. Candini, G. Lorusso, and M. Affronte
Nanotechnology 31, 274009 (2010).
Propagation of spin information at supra-molecular scale through hetero-aromatic linkers.
V. Bellini, G. Lorusso, A. Candini, W. Wernsdorfer, T. B. Faust, G. A. Timco, R.E.P. Winpenny, and M. Affronte
Phys. Rev. Lett. 106, 227205 (2011). Also selected as Editors’ Suggestion.