Decoding crystal growth kinetics and structural evolution in supercooled ZnSe by molecular dynamics simulation

L Separdar and JP Rino and ED Zanotto, COMPUTATIONAL MATERIALS SCIENCE, 212, 111598 (2022).

DOI: 10.1016/j.commatsci.2022.111598

Crystallization is a vital process in nature and technology; however, the detailed microscopic mechanisms of crystal nucleation and growth in most materials and the associated theoretical models are still elusive. In this work, we applied molecular dynamics (MD) simulations of spontaneous and seeded growth to infer the crystallization kinetics in supercooled zinc selenide (ZnSe) liquid - used as a model material for which an excellent interatomic potential already exists. ZnSe is a type II-VI semiconductor with a wide bandgap. We determined the growth velocity, upsilon(T), in a range of temperatures and the structural evolution of both inserted and spontaneously formed nuclei. By determining upsilon(T) at shallow supercooling using the seeding method and extrapolating towards deep supercooling, where spontaneous nucleation and growth could also be detected by MD, we showed that the most probable growth mechanism in ZnSe and the related theoretical model is the Normal Growth (N-model). We also followed the growth kinetics dependency on the crystallographic orientation. The structure of the final crystal in both approaches, seeded and spontaneous growth, at different supercoolings, is a mixture of the two most stable phases of this material: zinc blende and wurtzite, with predominance of the latter. These results shed light on unknown aspects of crystal growth in this important supercooled liquid and indicate the best theoretical model (N-model), which could be further tested for other materials using the proposed approach - MD simulations of seeded combined with spontaneous crystallization.

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