A method to identify partial phase transitions of bimetallic clusters through inequivalent sites from molecular dynamic simulations

The atomistic structure of clusters dictates their chemical activity, and its understanding is crucial when synthesizing and using them, particularly when working at often needed finite temperatures. The structural evolution becomes more intricate when the system contains more than one type of atom, such as in the case of bimetallic nanoparticles. We analyze the thermal evolution of the clusters through a simple approach, using molecular dynamics simulations to calculate the centrosymmetry parameter of each of the atoms. The atoms are then grouped into inequivalent sites according to the values of the parameter. This method allows us to map distinctive regions of the cluster structure and analytically track the structural evolution of individual sites and constituent regions in relation to the temperature in clusters with arbitrary spatial and chemical order. We show its application in Au-Cu nanoclusters, where we found partial melting temperatures and segregation temperatures for a range of morphologies and chemical compositions. This method reveals, through a simple calculation, the internal structure of nanoclusters at select temperatures as way of analyzing their behavior, facilitating their design and use on thermal applications.