Nucleation of crystals that are mixed composites of all three polymorphs in the Gaussian core model.
Nucleation of crystals that are mixed composites of all three polymorphs in the Gaussian core model.
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DOI：
10.1063/1.4922321
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发表时间：
2015-06
期刊：
影响因子：
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通讯作者：
J. Mithen;A. Callison;R. Sear
中科院分区：
文献类型：
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作者：
J. Mithen;A. Callison;R. Sear
我们提出了高斯核模型中的均匀晶体成核的计算机模拟结果。在我们的模拟中，我们研究了体心立方（bcc），面心立方（fcc）和六方密堆积晶体相之间的竞争。我们发现，从亚稳流体相形成的晶核是典型的“混合”，它们不包括一个单一的晶体多晶型。此外，当fcc相稳定或fcc和bcc相同样稳定时，发现这种混合性质持续远远超过成核势垒顶部的尺寸，即，远进入被认为是生长（而不是成核）的状态。因此，在该区域中，形成的多晶型物在成核之后很久才被选择。这是有影响的。当成核缓慢时，它将是结晶的限速步骤。然后，确定结晶时间尺度的步骤不同于控制哪种多晶型物形成的步骤。这意味着它们可以独立控制。同样在成核和多晶型选择之间，存在明显是结晶而不是流体的生长相，但是该相不能被分配给任何一种多晶型。
We present results of computer simulations of homogeneous crystal nucleation in the Gaussian core model. In our simulations, we study the competition between the body-centered-cubic (bcc), face-centered-cubic (fcc), and hexagonal-close-packed crystal phases. We find that the crystal nuclei that form from the metastable fluid phase are typically "mixed"; they do not consist of a single crystal polymorph. Furthermore, when the fcc phase is stable or fcc and bcc phases are equally stable, this mixed nature is found to persist far beyond the size at the top of the nucleation barrier, that is, far into what would be considered the growth (rather than nucleation) regime. In this region, the polymorph that forms is therefore selected long after nucleation. This has implications. When nucleation is slow, it will be the rate-limiting step for crystallization. Then, the step that determines the time scale for crystallisation is different from the step that controls which polymorph forms. This means that they can be independently controlled. Also between nucleation and polymorph selection, there is a growing phase that is clearly crystalline not fluid, but this phase cannot be assigned to any one polymorph.