Abstract
Can completely homogeneous nucleation occur? Large scale molecular dynamics simulations performed on a graphics-processing-unit rich supercomputer can shed light on this long-standing issue. Here, a billion-atom molecular dynamics simulation of homogeneous nucleation from an undercooled iron melt reveals that some satellite-like small grains surrounding previously formed large grains exist in the middle of the nucleation process, which are not distributed uniformly. At the same time, grains with a twin boundary are formed by heterogeneous nucleation from the surface of the previously formed grains. The local heterogeneity in the distribution of grains is caused by the local accumulation of the icosahedral structure in the undercooled melt near the previously formed grains. This insight is mainly attributable to the multi-graphics processing unit parallel computation combined with the rapid progress in high-performance computational environments.
Highlights
Can completely homogeneous nucleation occur? Large scale molecular dynamics simulations performed on a graphics-processing-unit rich supercomputer can shed light on this long-standing issue
Molecular dynamics (MD) simulations have been widely employed to clarify the nature of nucleation from an atomistic viewpoint
We have successfully applied a parallel graphics processing unit (GPU) computational scheme[34, 35] to very large scale molecular dynamics (MD) simulations of up to a billion atoms. By utilising this cutting-edge technique, here we investigate homogeneous nucleation from an undercooled iron melt using a large scale MD simulation
Summary
Can completely homogeneous nucleation occur? Large scale molecular dynamics simulations performed on a graphics-processing-unit rich supercomputer can shed light on this long-standing issue. A billion-atom molecular dynamics simulation of homogeneous nucleation from an undercooled iron melt reveals that some satellite-like small grains surrounding previously formed large grains exist in the middle of the nucleation process, which are not distributed uniformly. The existence of transient clusters during nucleation[17,18,19], estimation of the nucleation rate and the nucleation barrier[20,21,22], non-classical behaviour in nucleation[4, 5] and nucleation in nanoparticles[23, 24] have been investigated in detail by MD simulation These studies have successfully captured the local structure in the nucleation, most of them were limited to the formation of a single nucleus (or a few nuclei) owing to the computational limitation, except for several pioneering works[21, 25]. For consistency with previous studies[27,28,29,30,31,32,33], the nucleation from the undercooled iron melt is examined using the Finnis−Sinclair (FS) potential[36] (see Methods for more information)
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