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1. Crystal nucleation in an AlNiZr metallic liquid: Within and beyond classical nucleation theory

   https://doi.org/10.1016/j.actamat.2024.119860  

   Chen, Fangzheng; Sheng, Yelin; Dahlberg, Kian Cole; Nussinov, Zohar; Kelton, KF (May 2024, Acta Materialia)

   The Classical Nucleation Theory (CNT) has played a key role in crystal nucleation studies since the 19th century and has significantly advanced the understanding of nucleation. However, certain key assumptions of CNT, such as a compact and spherical nucleating cluster and the concept of individual diffusive jumps are questionable. The results of molecular dynamics (MD) studies of crystal nucleation in a Al 20 Ni 60 Zr 20 metallic liquid demonstrate that the nucleating cluster is neither spherical nor compact. The seeding method was employed to determine the critical cluster size and nucleation parameters from CNT, which were then compared to those derived from the Mean First Passage Time (MFPT) method. While the CNT-based nucleation rate aligns well with experimental data from similar metallic liquids, the MFPT rate differs significantly. Further, contrary to the assumption of individual jumps for atoms to join the nucleating cluster, a cooperative mechanism of attachment or detachment is observed. This is accompanied by synchronized changes in the local potential energy. Similar cooperative motion also appeared in a non-classical nucleation process, particularly during the coalescence of nuclei. 

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2. Dislocation nucleation in the phase-field crystal model

   https://doi.org/10.1103/PhysRevB.103.014107  

   Skogvoll, Vidar; Skaugen, Audun; Angheluta, Luiza; Viñals, Jorge (January 2021, Physical Review B)

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3. Reversible disorder-order transitions in atomic crystal nucleation

   https://doi.org/10.1126/science.aaz7555  

   Jeon, Sungho; Heo, Taeyeong; Hwang, Sang-Yeon; Ciston, Jim; Bustillo, Karen C.; Reed, Bryan W.; Ham, Jimin; Kang, Sungsu; Kim, Sungin; Lim, Joowon; et al (January 2021, Science)

   Nucleation in atomic crystallization remains poorly understood, despite advances in classical nucleation theory. The nucleation process has been described to involve a nonclassical mechanism that includes a spontaneous transition from disordered to crystalline states, but a detailed understanding of dynamics requires further investigation. In situ electron microscopy of heterogeneous nucleation of individual gold nanocrystals with millisecond temporal resolution shows that the early stage of atomic crystallization proceeds through dynamic structural fluctuations between disordered and crystalline states, rather than through a single irreversible transition. Our experimental and theoretical analyses support the idea that structural fluctuations originate from size-dependent thermodynamic stability of the two states in atomic clusters. These findings, based on dynamics in a real atomic system, reshape and improve our understanding of nucleation mechanisms in atomic crystallization. 

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4. Machine learning for molecular simulations of crystal nucleation and growth

   https://doi.org/10.1557/s43577-022-00407-1  

   Sarupria, Sapna; Hall, Steven W; Rogal, Jutta (January 2022, MRS bulletin)

   Molecular simulations are a powerful tool in the study of crystallization and polymorphic transitions yielding detailed information of transformation mechanisms with high spatiotemporal resolution. How- ever, characterizing various crystalline and amorphous phases as well as sampling nucleation events and structural transitions remain extremely challenging tasks. The integration of machine learning with molecular simulations has the potential of unprecedented advancement in the area of crystal nucleation and growth. In this article, we discuss recent progress in the analysis and sampling of structural trans- formations aided by machine learning and the resulting potential future directions opening in this area. 

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5. RSeeds: Rigid Seeding Method for Studying Heterogeneous Crystal Nucleation

   https://doi.org/10.1021/acs.jpcb.3c00910  

   Yuan, Tianmu; DeFever, Ryan S; Zhou, Jiarun; Cortes-Morales, Ernesto Carlos; Sarupria, Sapna (May 2023, The Journal of Physical Chemistry B)

   Heterogeneous nucleation is the dominant form of liquid-to-solid transition in na- ture. Although molecular simulations are most uniquely suited to study nucleation, the waiting time to observe even a single nucleation event can easily exceed current computational capabilities. Therefore, there exists an imminent need for methods that enable computationally fast and feasible studies of heterogeneous nucleation. Seeding is a technique that has proven successful at dramatically expanding the range of computationally accessible nucleation rates in simulation studies of ho- mogeneous crystal nucleation. In this paper, we introduce a new seeding method for heterogeneous nucleation called Rigid Seeding (RSeeds). Crystalline seeds are treated as pseudo-rigid bodies and simulated on a surface with metastable liquid above its melting temperature. This allows the seeds to adapt to the surface and identify favorable seed–surface configurations, which is necessary for reliable predictions of crystal polymorphs that form and the corresponding heterogeneous nucle- ation rates. We demonstrate and validate RSeeds for heterogeneous ice nucleation on a flexible self-assembled monolayer surface, a mineral surface based on kaolinite, and two model surfaces. RSeeds predicts the correct ice polymorph, exposed crystal plane, and rotation on the surface. RSeeds is semiquantitative and can be used to estimate the critical nucleus size and nucleation rate when combined with classical nucleation theory. We demonstrate that RSeeds can be used to evaluate nucleation rates spanning many orders of magnitude. 

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