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Abstract

Molecular dynamics simulations can provide valuable atomistic insight into solidification, but the modelling of the initial nucleation during solidification remains challenging due to the extended timescales of the process. Nowadays, advanced computational methods like transition path sampling (TPS) have enabled the investigation of nucleation on the atomistic level. In this work, we employ TPS to investigate the nucleation during solidification in nickel. We initially focus on homogeneous nucleation in elemental nickel as a function of undercooling. As a second step towards more complex materials, we extend our study by including small Ni-clusters as seeds during heterogeneous nucleation. The transition state ensemble obtained from our TPS simulations provides atomistic insight into the structure and size of critical nuclei for different nucleation mechanisms (homogeneous and heterogeneous nucleation at defects), as well as nucleation barriers/rates. Such results provide valuable information to validate and improve existing thermodynamic models describing nucleation. Furthermore, the information obtained about nucleation rates and the distribution of nucleation centres can also directly be connected to phase field models.