Fig. 5-7 Relation of the binding potential energy for the uranium dimer to interatomic distance (angstrom) This result shows the highest structural stability at interatomic distance 2.31 for metallic uranium dimer.

Fig. 5-8 Predicted structure of metallic uranium microcluster, computed by molecular-dynamic simulations (Equilibrium structures of uranium microcluster containing n=3 - 137 atoms)

It is well known that the structural stability of an aggregate composed of metal atoms, i.e. a metallic microcluster, varies with the number of atoms in the cluster. By controlling the form of the metallic microcluster form a few atoms up to thousands, it is possible to design advanced materials which are different from the bulk solids. Uranium has been used as nuclear fuel, and recently, some uranium intermetallic compounds have been found to be superconducting. A lot of research has been carried out on the physical and chemical properties of these compounds. In order to understand these properties, information on the electronic structure and stability of uranium metallic clusters has become more important. We have carried out first principle electronic structure calculations for the uranium dimer and obtained the relationship between binding energy and interatomic distance (Fig. 5-7). By using the relation between the binding energy and interatomic distance, we have simulated the aggregation of uranium atoms using molecular dynamics simulations. Figure 5-8 shows predicted stable uranium microstructures. It was found that uranium clusters containing 3, 4, 5, 6, 7 and 13 atoms have highly symmetric stable structures. We also simulated the aggregation of uranium atoms to the crystal structure by increasing the number of atoms. Transuranium elements, i.e. the elements heavier than uranium, may have attractive characteristics. The information obtained from our research is likely to be very useful in basic studies of both the physical and chemical properties of these elements.

Reference S. Erkoc et al., Molecular-Dynamics Simulations of Uranium Microclusters, J. Phys. Jpn., 68(2), 440 (1999).

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