Structural, Electronic, and Magnetic Properties of Iron Disulfide FenS20/± (n = 1-6) Clusters.

The structural, electronic, and magnetic properties of neutral and charged FenS20/± (n = 1-6) clusters have been calculated in the framework of the density functional theory in the generalized gradient approximation for the exchange and correlation. The calculated adiabatic electron affinity and the vertical detachment energy are found to be in good agreement with the available experimental data. The impact of disulfide-doping of small iron clusters on the atomic structure, stability, magnetic moment, and reactivity is determined through the analysis of the binding energy per atom, electronic charge transfer, spin-polarized electronic densities of states, and global reactivity indicators like the electronegativity and chemical hardness. Our results provide an exhaustive characterization of these small iron-sulfide particles under vacuum, which is the first step to completely understand their role as components of proteins.

Density functional study of the structures and electronic properties of nitrogen-doped Ni(n) clusters, n = 1-10.

We present a first-principles study of the equilibrium geometries, electronic structure, and related properties (binding energies, ionization potentials, electron affinities, and magnetic moments) of free-standing Ni(n) (n = 1-10) clusters doped with one impurity of N. Calculations have been performed in the framework of the density functional theory, as implemented in the SIESTA code within the generalized gradient approximation to exchange and correlation. We show that, in contrast to the molecular adsorption of N(2), the adsorption of a single N atom can dramatically change the structure of the host Ni(n) cluster, examples of which are Ni(5)N, Ni(7)N, and Ni(10)N, and that noticeable structure relaxations take place otherwise. Doping with a nitrogen impurity increases the binding energy as well as the ionization potential (except for Ni(6)N), which proves that N-doping works in favor of stabilizing the Ni clusters. We also find that the magnetic moments decrease in most cases upon N-doping despite the fact that the average Ni-Ni distance increases. The HUMO-LUMO gap for one spin channel strongly changes as a function of size upon N-doping, in contrast with the HUMO-LUMO gap for the other spin channel. This might have important implication in electronic transport properties through these molecular contacts anchored to source and drain electrodes.