Tetrahedral Stacking of Copper in Its Incubation Period of Crystallization: A Study of Large-Scale Molecular Dynamics Simulation

Tetrahedral stacking of atoms has great importance for melt stability, crystallization, and glass formation. For example, the spiral chain of close-packed tetrahedra was considered as a pseudonucleus for crystallization. Tetrahedral stacking can yield icosahedral or helical structures, which are seen in the self-organized superstructures of nano- or colloidal particles. Previous studies have mostly focused on tetrahedral packings that lead to a form with high-order symmetry, but imperfect tetrahedral stacking, which is common in practice, has rarely been studied. Here, we annealed pure copper in order to analyze the growth of a seeded 5-fold twinning structure made up of three tetrahedra over the incubation period. To do this, we used a superlarge system made up of 55 million atoms in molecular-dynamics simulations. The tetrahedral stacking gives rise to a chainlike structure that is capable of being described by a three-element coding scheme. The findings imply that the melt stability can be improved, even if the stacking structure of tetrahedra lacks high-order symmetry.