Structural, Electronic, and Magnetic Properties of Small Ni Clusters

Abstract

The electronic structure and magnetic properties of small Ni n clusters (n = 4, 5, 6, 8, 13) are studied at the self-consistent-field multireference configuration interaction singles level using the intermediate neglect of differential overlap model Hamiltonian parametrized for spectroscopy. Results are in agreement with density functional theory calculations and ab initio calculations for the smaller (n = 4−6) structures. Discrepancies develop for the larger (n = 8, 13) structures, and these discrepancies are discussed. We examine systems and criteria for the selection of the cluster size that most accurately model heterogeneous catalysts.

Projected Unrestricted Hartree−Fock Calculations and the Magnetism of Large Nickel Clusters

“…Results of Tables 1-4 show that, at both levels of calculation, high multiplicities (M) characterize both symmetries. As previously discussed in ref 19, no distortions are predicted by the ROHF/MRCI calculations for the 7 A 1g low energy state in D 4h symmetry. In T d symmetry, on the other hand, the symmetry is lowered to C 3V through elongation along a 3-fold axis due to the nonequivalent occupation of the 3-fold degenerate t orbitals.…”

“…Details of the procedure, regarding the number of references, the symmetry imposed on the calculations, and the size of the resulting CI have been already discussed in ref 19. The results are repeated here only for comparative purposes.…”

“…This statement is particularly true when dealing with nanometric clusters, where the geometry and multiplicity of the structure calculated as most stable, for a given cluster size, still remains dependent on the calculation procedure. 7, [19][20][21][22] Even within a given methodology, different basis sets in an ab initio or density functional calculation result in different geometries for a given cluster size, and the associated electronic descriptions will not be, thence, even comparable.…”

“…For the smaller clusters (n ) 4, 6,8,13) we have considered Ni structures built up on the interatomic bulk distance and on the value derived from a full geometry optimization, comparing the results with previous data derived from ROHF-MRCI calculations, 19 searching for the best way of dealing with the open-shell electronic distributions that are strongly related to reactivity. Larger clusters (n ) 20, 51) have been used to model trilayer and bilayer surface-like systems.…”

Amorphous Silica as a Versatile Supermolecular Ligand for NiII Amine Complexes: Toward Interfacial Molecular Recognition

“…The semiempirical quantum code ZINDO (Accelerys software) was used. [32,33] Elemental analyses: Elemental analyses (Ni and Si) were performed by the Service Central d'Analyse du CNRS, Vernaison. For reference salts, all elements were analyzed to confirm the stoichiometry of the Ni II complexes.…”