Maximum Likelihood Analysis of Reaction Coordinates during Solidification in Ni.

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Physics

Background:

• Classical Nucleation Theory (CNT) describes homogeneous nucleation via random fluctuations, assuming nucleus size as the sole reaction coordinate (RC).
• Many materials exhibit complex crystallization pathways, forming different polymorphs, necessitating more sophisticated RCs.
• Understanding nucleation mechanisms is crucial for predicting and controlling material properties.

Purpose of the Study:

• To identify suitable reaction coordinates (RCs) for the nucleation mechanism during solidification in Nickel (Ni).
• To investigate deviations from Classical Nucleation Theory (CNT) in Ni crystallization.
• To elucidate the role of prestructured liquid regions in the nucleation process.

Main Methods:

• Employed transition path sampling (TPS) to explore nucleation pathways.
• Utilized maximum likelihood analysis of candidate order parameters to identify key variables.
• Analyzed a reweighted path ensemble to understand the nucleation mechanism.

Main Results:

• Identified a prestructured liquid region surrounding crystal clusters as a relevant order parameter.
• Demonstrated that this prestructured liquid enhances the RC, playing a key role in nucleus description and interfacial free energy.
• Showed that prestructured liquid clusters act as precursors in a nonclassical two-step crystallization mechanism.

Conclusions:

• The nucleation mechanism in Ni deviates from CNT, involving a nonclassical two-step process.
• Prestructured liquid regions are crucial precursors that influence the nucleation pathway and polymorph selection.
• The identified RCs provide a more comprehensive description of the nucleation process and interfacial properties.