Structures of small alkali-metal clusters

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Abstract
Structures of clusters of monovalent metals have been calculated using the Kohn-Sham method in the local-density approximation. The metal atoms are described by a local pseudopotential. Instead of using any basis-set expansion, the single-electron wave functions are solved on a three-dimensional grid using a relaxation method. Since the relaxation method is also used to solve the Poisson equation, the electronic structure as well as the ion positions can be relaxed simultaneously for finding the ground-state configuration. The structures obtained for small clusters (N<8) agree well with the results of earlier calculations. These structures are found to be independent of the pseudopotential parameter and common to all alkali metals. It is shown that the geometries of these clusters are similar to those of small clusters of electron-hole plasma, and can be understood in terms of single-electron states in a spherical potential (jellium model). The electric polarizabilities of the clusters are calculated and the results agree well with the experimental results. For a diatomic cluster the two-electron wave function is solved exactly in the finite grid and the results are compared with those obtained using the local-density approximation.