Metadynamics for solid-liquid coexistence system of binary alloys

A new metadynamics-based method is proposed to accurately model solute partitioning behavior and determine the solid-liquid interfacial energy in binary alloys. The method improves the identification of body-centered cubic (BCC) crystal structure at high temperatures by revising the definition of the collective variable (CV). The solid-liquid interfacial energy is determined from the free energy surface (FES) differences by performing metadynamics simulations on two systems with different sizes but identical compositions. The excess energy due to the solid-liquid interface was clearly separated from the free energy of mixing thanks to the identical chemical potential of solid and liquid phases in these two systems. The method is applied to Fe-C alloys, where no significant dependence of interfacial energy on carbon concentration is observed within the investigated temperature range. Moreover, the method is applied to several substitutional BCC and face-centered cubic (FCC) alloys, demonstrating its versatility and potential for broader application to other alloys. The origin of the convex downward shift in the FES at the solid-liquid coexistence state is discussed from a thermodynamic perspective. This study contributes to the understanding of metadynamics in alloy systems by providing a thermodynamic justification.