Types of Size-Dependent Melting in Fe Nanoclusters: a Molecular Dynamics Study

Metallic nanoclusters are of interest in many fields because of their size-dependent catalytic activity. This activity can, in part, be influenced by their melting properties. In this work, the melting phase transitions of $Fe_{n}$ nanoclusters with $n \leq 100$ atoms were investigated using classical many-body molecular dynamics simulations. Adding a single atom to many cluster sizes induced strong variations in melting point ($T_{melt}$), latent heat of melting ($\Delta H_{melt}$), and onset temperature of isomerization ($T_{iso}$). Clusters with size-dependent melting behavior were classified into 3 distinct cluster types: closed-shell, near-closed-shell, and far-from-closed-shell clusters. First-order-like phase transitions were observed only for cluster sizes with particularly symmetric closed shells and near-closed shells with up to a few missing or extra atoms. Near-closed-shell clusters had very low $T_{iso}$ relative to their $T_{melt}$. Far-from-closed-shell clusters exhibited second-order-like phase transitions. Variations in the melting and isomerization behavior of neighboring cluster sizes may have implications for catalytic systems such as the growth of single-wall carbon nanotubes.