First-principles studies are cartied out on the electronic structure aed Compton profile for the low-synmmetry system of calcium dihydride using the discrete variational local-density-funational method with embedded cluster model. The results demonstrate that, with the ionic bonding picture, experimental data from photoelectron spectroscopy with both x-rays and synchrotron radiation and from Compton profile measurernents can be reasonably understood. Based on the bonding chacter revealed in the electronic stntcture, we suggest that CaHz doped with a monovalent element could be a superconductor.

The magnetic properties of icosahedral MRu12 clusters are studied using the discretevariational local-spin-density-functional method, where M=V, Cr, Mn, Fe, Co, and Ni. The results show that all of the Ih MRu12 clusters, just like the case for the Ih Ru13 cluster, have double magnetic solutions. In contrast to the moment of 4μB for the Ih Ru13 cluster, the total magnetic moments of the Ih MRu12 clusters, ranging from 1μB to 20μB, have been changed greatly by the substitution of the central Ru atom with M. Among them, the NiRu12 cluster has a giant moment of 20μB. Furthermore, the NiRu12 cluster has nondegenerate ground state and could be expected to be remarkably stable. Therefore, for the purpose of enhancing the magnetic moment of the Ih Ru13 cluster, Ni is a promising candidate as a dopant. Finally, we predict that all the Ih MRu12 clusters except NiRu12 might belong to the class in which the magnetization of the cluster increases with temperature.

The magnetic properties of 13-atom M clusters (M=Y, Zr, Nb, Mo, and Tc) with three possible highsymmetrygeometries have been studied using the discrete-variational local-spin-density-functional method. While the ground states of most transition-metal 13-atom clusters correspond to the icosahedral structure, we found that the cuboctahedral structure is more energetically stable than the icosahedral one for Mo13 and Tc13 clusters. The ground states of all the clusters are shown to be magnetic, but their magnetic moments are not striking.

The electronic properties and magnetism of RuN clusters (N54, 6, 10, 13, 19, 43, and 55) are studied using the discrete-variational local-spin-density-functional method. The bond lengths in the clusters with N<13 are optimized, and the cluster binding energies are found to increase monotonically with the increase of cluster size. All clusters except Ru19 are shown to have magnetic ground states. The average magnetic moments per atom for the RuN are found to decrease rapidly with the increase of the cluster size, although small oscillation exists. The calculated moments per atom for Ru10 and Ru13 clusters are in good agreement with the experimental values. Multiple magnetic solutions are explored, and double magnetic solutions are found for the icosahedral (Ih) Ru13 cluster which is used successfully to eliminate the contradiction between the previous theory and experiment on the moment of Ru13 cluster. The electronic structures of RuN clusters are calculated, and indicate that all clusters are metallic in behavior. The comparison between the Ru55 cluster and the bulk counterpart indicates that Ru55 has shown bulklike properties in the binding energy, magnetism, valence-bandwidth, and density of states. Based on electronic-structure results, the reactivity of Ru6, Ru19, and Ru43 clusters toward H2, N2, and CO molecules is predicted.

Local spin-density-functional calculations are performed to study the geometric and electronic structure of PbNa6 clusters. Three possible isomeric structures are examined. Both the electronic and the geometric factors are shown to be important to the stabilization of the cluster and the most stable structure is found to be a tricapped tetrahedron. The electronic structure of this cluster indicates that the metallic bonding interaction of delocalized electrons is responsible for the exceptional stability of the cluster.