On the microscopic description of sublimation and sublimation-driven melting in gold nanoparticles

High temperature, high vacuum in situ experiments on gold nanoparticles repeatedly reveal an inherently non-equilibrium evolution characterised by surface atom ejection (sublimation), shrinkage, a solid-to-liquid transition (melting) after sufficient mass loss, and evaporation of the resulting droplet until disappearance. Existing theoretical and simulation descriptions of this non-equilibrium sequence rely on the assumptions of homogeneous equilibrium thermodynamics and therefore fail to clearly identify the structural and dynamical changes that accompany the observed transitions. In this work, we establish a molecular dynamics (MD) framework that reproduces both the experimental setup and phase evolution, and identifies where and when sublimation and melting occur. From the generated MD trajectories, we extract: distribution, correlation and displacement functions, density profiles, kind of atomic motion in each nanoparticle shell. This information and the analysis thereof allow the reproduction of the experimental sequence of phase transitions and the determination of both the sublimation onset temperature and the temperature at which the melting process is complete, in quantitative agreement with experiment. The results demonstrate the importance of an appropriate choice of interaction potential and provide a numerical framework that can be extended and applied to other materials.