Bond orientational ordering in a metastable supercooled liquid: a shadow of crystallization and liquid–liquid transition
Bond orientational ordering in a metastable supercooled liquid: a shadow of crystallization and liquid–liquid transition
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DOI：
10.1088/1742-5468/2010/12/p12001
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发表时间：
2010-12
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影响因子：
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通讯作者：
Hajime Tanaka
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作者：
Hajime Tanaka
人们普遍认为，液态可以用单序参数（密度）来表征，并且从液体到固体的转变可以通过密度排序（平移排序）来描述。例如，这类理论在描述硬球的相行为方面取得了巨大成功。然而，这些理论无法捕捉到一些特征。例如，硬球结晶成 hcp 或 fcc 结构，没有 bcc 有序的趋势，这是基于密度有序参数的朗道型自由能的 Alexander-McTague 理论所预期的。我们还在亚稳态过冷液体中发现了类似 hcp 的键取向排序，这促进了 hcp 晶体的成核。此外，基于单阶参数的理论无法解释单组分液体中液体和液-液转变的类水热力学和动力学异常。基于这些事实，我们认为我们需要一个额外的有序参数来描述液态。它是键取向有序，是由硬球中的致密堆积或分子和原子液体中的定向键引起的。键取向顺序本质上是局部性质的，与具有全局性质的平移顺序不同。这一特征在结晶和准晶形成中发挥着独特的作用。我们还揭示了键取向有序性是玻璃化转变附近动态异质性的原因，并且与缓慢的动力学有关。与此相关，我们注意到，为了描述高度无序液体的结构，我们需要低构型熵的结构特征，这比键取向顺序更普遍。最后，类水异常和液-液转变可以分别通过氢键或共价键及其协同作用导致的键取向排序来解释。因此，我们认为键取向有序是物理理解结晶、准结晶、玻璃化转变、类水异常和液-液转变的关键。沿着这条线索对这些现象进行统一的描述是可能的。
It is widely believed that a liquid state can be characterized by a single order parameter, density, and that a transition from a liquid to solid can be described by density ordering (translational ordering). For example, this type of theory has had great success in describing the phase behaviour of hard spheres. However, there are some features that cannot be captured by such theories. For example, hard spheres crystallize into either hcp or fcc structures, without a tendency of bcc ordering which is expected by the Alexander–McTague theory based on the Landau-type free energy of the density order parameter. We also found hcp-like bond orientational ordering in a metastable supercooled liquid, which promotes nucleation of hcp crystals. Furthermore, theories based on the single order parameter cannot explain water-like thermodynamic and kinetic anomalies of a liquid and liquid–liquid transition in a single-component liquid. Based on these facts, we argue that we need an additional order parameter to describe a liquid state. It is bond orientational order, which is induced by dense packing in hard spheres or by directional bonding in molecular and atomic liquids. Bond orientational order is intrinsically of local nature, unlike translational order which is of global nature. This feature plays a unique role in crystallization and quasicrystal formation. We also reveal that bond orientational ordering is a cause of dynamic heterogeneity near a glass transition and is linked to slow dynamics. In relation to this, we note that, for describing the structuring of a highly disordered liquid, we need a structural signature of low configurational entropy, which is more general than bond orientational order. Finally, the water-like anomaly and liquid–liquid transition can be explained by bond orientational ordering due to hydrogen or covalent bonding and its cooperativity, respectively. So we argue that bond orientational ordering is a key to the physical understanding of crystallization, quasicrystallization, glass transition, water-like anomaly and liquid–liquid transition. A unified description of these phenomena may be possible along this line.