Stabilities of large sodium clusters for different atomic arrangements

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Abstract
We have used density-functional theory and the spherically averaged pseudopotential (SAPS) model to study the relative stabilities of large sodium clusters with different atomic arrangements. Starting with perfect crystallinelike clusters with filled atomic shells, we find that small distortions of the geometry strongly enhance their stability. However, in the size range studied in this paper (N≤340) the distorted-crystalline structures are not the absolute energy minima. These are, instead, noncrystalline structures obtained by energy minimization without any structural constraints. In particular, noncrystalline clusters with enough electrons to fill electronic shells are the most stable ones. The crossover between magic numbers of electronic origin (clusters with filled electronic shells) and magic numbers of atomic origin (crystalline structures with filled atomic shells) has not yet taken place in the size range studied here and should occur for larger sizes.