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Abstract

Crystal nucleation is a key step during solidification and polymorph selection in metals. Here we employ transition path sampling simulations and maximum likelihood analysis to identify the reaction coordinates of the nucleation mechanism in Ni. As a second step, we investigate the influence of small prestructured seeds on the nucleation process. Our analysis shows that the nucleation pathway is governed by an initial formation of prestructured liquid regions and a subsequent emergence of fcc-hcp crystallites within the core of the clusters. The prestructured region enhances the reaction coordinate and predetermines the polymorphs selected during crystallization. Consistently, the presence of fcc and hcp seeds enhances the nucleation rate and determines the structure of the growing nuclei, while icosahedral and bcc seeds have no effect on the mechanism. Our results highlight the prominent role of the prestructured liquid region and impurities during crystallization in Ni.