Size-dependent Melting Behavior of Iron Nanoparticles by Replica Exchange Molecular Dynamics

Due to the finite size effect, nanoparticles own unique physical, chemical, and magnetic properties. Comparing with the bulk materials, the large surface/volume ratio of nanoparticles could lead to more complicate atomic and electronic behavior, thus the thermodynamical properties can be also very rich. In the last a few decades, as one of the fundamental problems in the nano science, the melting behavior of nanoparticles had been widely investigated by numerous experimental and theoretical studies. Using replica-exchange molecular dynamics method (REMD), we have investigated the size dependence of the melting behavior of iron nanoparticles. Comparing to the conventional molecular dynamics (MD), the REMD method is found to be very efficient to determine the melting point, by avoiding the superheating and undercooling phenomena. With accurate determination of the melting point, we find that the melting temperature does not follow linearly with the inverse of size. By incorporating the size dependent thickness of surface liquid layer which is observed in our simulation, we propose a revised liquid skin melting model to describe the size dependent melting temperature.