Computational study of phase transitions in ultra-small copper nanoparticles under ultra-high cooling rates using COMB3 potential

Abstract Traditional interatomic potentials in molecular dynamics simulations, relying on fixed charges, often fail to capture dynamic charge redistribution crucial for surface phenomena. This limitation is particularly pronounced in ultra-small nanoparticles, given their high surface-to-volume ratio and broken symmetry. Here, we conducted a computational study on the phase transitions and structural evolution of copper nanoparticles of varying sizes, specifically under ultra-high cooling rates. Utilizing the third-generation Charge-Optimized Many-Body (COMB3) potential, which dynamically calculates atomic charges, our simulations provided a more realistic description of surface effects and non-equilibrium processes. This revealed a size-dependent liquid–solid phase transition characterized by stable charge ordering and persistent surface electrical dipoles. In the solid state, an amorphous surface formed below the solidification temperature, subsequently becoming crystalline at lower temperatures. The highest magnitude charges are localized at crystalline plane contours, suggesting potentially reactive sites. Graphical abstract