Thermodynamics of nanoparticle coalescence at different temperatures via well-tempered metadynamics

Abstract

The coalescence of two nanoparticles is a fundamental process that plays a dominant role in the formation of new nanoparticles. It constitutes a direct way to synthesize bimetallic nanoparticles with the continuous growth of potential applications. However, a full mechanistic comprehension that will allow us to predict and control the coalescence result has not been achieved yet. Probably, the main reason for this is the complexity of the whole process, which brings together several elementary subprocesses like segregation, surface reduction, structural stress, or even changes of ordered states, which present a large complexity by themselves. It is particularly important for computer simulations to consider the fact that the mixing or segregation of components occurs trough many diffusion events, which constitute rare events. These processes require advanced methods to accelerate their sampling. In the present work, we use well-tempered metadynamic simulations to describe the thermodynamics of the coalescence of Au42 and Co13 clusters at different temperatures. We show several free-energy, entropy, and enthalpy profiles and discuss in detail their particular features. We also propose to rationalize the observed behavior in terms of the calorimetric curves of the product and the reactant nanoparticles involved.