Building Clusters Atom-by-Atom : From Local Order to Global Order

We have carried out extensive density functional calculations for series of sodium clusters Na N ranging from N = 10 to 147 and have obtained ≈13 000 distinct isomers. We unravel a number of striking features of the growth characteristics. The growth shows an order-disorder-order pattern of cyclic nature. Between two ordered clusters, the growth proceeds via disordered clusters having multicentered icosahedral local order. The global order emerges suddenly with the addition of one or two atoms only. The clusters around N = 92, the electronically closed shell system, behave completely differently and do not show the favored icosahedral local order. It is the absence of icosahedral local order that is responsible for the rather low melting temperatures observed in the experiments.