Stepwise Melting in Na41+: A First-Principles Critical Analysis of Available Experimental Results

Current experimental techniques for measuring the heat capacity of size-selected and isolated atomic clusters are based on dissociation and differ in the critical step of deducing internal energy changes from the dissociation measurements. The heat capacity of Na41+ has been measured by two different techniques with uneven results: one suggests a gradual melting process with a featureless heat capacity; the other reports the first observation of two-step melting in sodium clusters. Here, we report first-principles molecular dynamics simulations of the melting transition in Na41+, including an approximate account of quantum atomic delocalization effects. Our work aims to help in the resolution of the experimental discrepancies. The results provide support for a stepwise melting process, which is induced by a hierarchical structure of the energies of local minima in the potential enery landscape.