Building clusters atom by atom: from local order to global order

TL;DR

This study uses density functional calculations to analyze sodium clusters from 10 to 147 atoms, revealing a cyclic pattern of order-disorder transitions and the sudden emergence of global order with minimal atom additions.

Contribution

It uncovers the growth pattern of sodium clusters, highlighting the cyclic order-disorder-order transitions and the unique behavior of closed-shell clusters around N=92.

Findings

Growth shows cyclic order-disorder-order pattern.

Global order appears suddenly with one or two atom additions.

Clusters around N=92 lack icosahedral local order, affecting melting temperatures.

Abstract

We have carried out extensive density functional calculations for series of sodium clusters $Na$$_{N}$ ranging from $N$=10 to 147 and have obtained $\approx$ 13000 distinct isomers. We unravel a number of striking features of the growth characteristics. The growth shows order-disorder-order pattern of cyclic nature. Between two ordered clusters the growth proceeds via disordered clusters having multi-centered 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 which is responsible for rather low melting temperatures observed in the experiments.