Anomalous Size Dependence in the Melting Temperatures of Free Sodium Clusters: An Explanation for the Calorimetry Experiments

Abstract

The meltinglike transition in unsupported NaN clusters (N=55, 92, 147, 181, 189, 215, 249, 271, 281 and 299) is studied by first-principles isokinetic molecular dynamics simulations. The irregular size dependence of the melting temperatures Tm observed in the calorimetry experiments of Schmidt et al. [ Nature (London) 393 238 (1998)] is quantitatively reproduced. We demonstrate that structural effects alone can explain all broad features of experimental observations. Specifically, maxima in Tm(N) correlate with high surface stability and with structural features such as a high compactness degree.