Transition-metal Nanoclusters

The last decade has witnessed the rapid development of a new field of research - nanoscience. Among nanodimensional objects, nanoclusters occupy a very important place. Nanoclusters are aggregates of atoms or molecules, containing between less than 10 and 106 constituent particles. Possible applications of nanoclusters range from catalysis to spintronics, with clusters formed by transition-metal atoms playing a particularly important role. This project is devoted to ab-initio investigations of the structural, physical and chemical properties of transition- metal nanoclusters, both in the gas-phase and supported on metallic or insulating substrates, using density functional techniques. Recent studies of small clusters of late transition metals have shown that most current theoretical investigations are subject to two main limitations: (i) As a consequence of the complex metallo-covalent bonding forces, only dynamical simulations allow to discover the sometimes rather surprising equilibrium structures of the clusters. (ii) At present, there is still a rather substantial gap between the experimentally measured magnetic moments and even the best ab-initio calculations. It has been suggested that a quantitative evaluation of the cluster moments requires a determination of the orbital moment using fully relativistic calculations (including spin-orbit coupling). One of the first goals of this project will be the investigation of the orbital contribution to the magnetic moment of free Fe, Co, Ni, Pd, and Pt clusters, based on a simultaneous optimization of all geometric and magnetic degrees of freedom. The technological relevance of small magnetic clusters depends on the existence of a high magnetic moments and of a magnetic anisotropy energy large enough to supress superparamgnetic fluctuations. As a possible way to satisfy both requirement, we will investigate alloy clusters of 3d and 4d (or 5d) metals: The 3d-metal contributes the high moment, the heavy metal the strong spin-orbit coupling. The properties of clusters deposited on metallic or oxidic supports are strongly influenced by cluster-support interactions. We will perform a comparative investigation of the structures and of the physico-chemical properties of clusters produced by soft landing from the gas-phase and by sequentail aggregation of atoms. We will concentrate on the magnetic properties of clusters supported on metallic nonmagnetic substrates and on the chemical reactivity of clusters anchored on oxidic supports.

The last decade has witnessed the rapid development of a new field of research - nanoscience. Among nanodimensional objects, nanoclusters occupy a very important place. Nanoclusters are aggregates of atoms or molecules, containing between less than 10 and 106 constituent particles. Possible applications of nanoclusters range from catalysis to spintronics, with clusters formed by transition-metal atoms playing a particularly important role. This project is devoted to ab-initio investigations of the structural, physical and chemical properties of transition- metal nanoclusters, both in the gas-phase and supported on metallic or insulating substrates, using density functional techniques. Recent studies of small clusters of late transition metals have shown that most current theoretical investigations are subject to two main limitations: (i) As a consequence of the complex metallo-covalent bonding forces, only dynamical simulations allow to discover the sometimes rather surprising equilibrium structures of the clusters. (ii) At present, there is still a rather substantial gap between the experimentally measured magnetic moments and even the best ab-initio calculations. It has been suggested that a quantitative evaluation of the cluster moments requires a determination of the orbital moment using fully relativistic calculations (including spin-orbit coupling). One of the first goals of this project will be the investigation of the orbital contribution to the magnetic moment of free Fe, Co, Ni, Pd, and Pt clusters, based on a simultaneous optimization of all geometric and magnetic degrees of freedom. The technological relevance of small magnetic clusters depends on the existence of a high magnetic moments and of a magnetic anisotropy energy large enough to supress superparamgnetic fluctuations. As a possible way to satisfy both requirement, we will investigate alloy clusters of 3d and 4d (or 5d) metals: The 3d-metal contributes the high moment, the heavy metal the strong spin-orbit coupling. The properties of clusters deposited on metallic or oxidic supports are strongly influenced by cluster-support interactions. We will perform a comparative investigation of the structures and of the physico-chemical properties of clusters produced by soft landing from the gas-phase and by sequentail aggregation of atoms. We will concentrate on the magnetic properties of clusters supported on metallic nonmagnetic substrates and on the chemical reactivity of clusters anchored on oxidic supports.