Signatures of distinct dynamical regimes in the energy landscape of a glass-forming liquid
Signatures of distinct dynamical regimes in the energy landscape of a glass-forming liquid
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DOI：
10.1038/31189
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发表时间：
1998-06
期刊：
影响因子：
64.8
通讯作者：
S. Sastry;P. Debenedetti;F. Stillinger
中科院分区：
文献类型：
--
作者：
S. Sastry;P. Debenedetti;F. Stillinger
在适当的制备方法下，大多数材料在低温下达到玻璃化状态。这种状态表现出固体的力学性质，但表现出微观结构无序。然而，对这种玻璃状态的全面理解仍然缺乏。一个普遍的假设是，在玻璃动力学中观察到的非指数弛豫过程--以及在蛋白质动力学、蛋白质折叠和种群动力学中观察到的--(与复杂动力学的其他表现一样)受到与系统可能采用的结构构型相关的潜在能量格局的强烈影响。但在玻璃形成的研究中，这方面的具体证据一直很少。在这里，我们提供了这样的证据，这些证据是从一个模型玻璃形成液体的计算机模拟中获得的。我们证明，非指数松弛的开始对应于一个明确定义的温度，在该温度下，液体所探测的势能极小值的深度随着温度的降低而增加，而在该温度以上则不随温度的降低而增加。在较低的温度下，当液体被困在最深的可到达的能量盆地时，我们观察到一个急剧的转变。这种转变温度取决于冷却速度，类似于实验中的玻璃化转变。我们还提供了证据表明，液体采样的势能极小值的势垒高度在玻璃化转变以上的温度下突然增加，但远低于非指数弛豫开始的温度。这种对能量景观的静态、地形特征和复杂动力学之间的关系的识别，有望对玻璃化转变有更清晰的、可能是热力学的理解。
Most materials attain a glassy state at low temperatures under suitable methods of preparation. This state exhibits the mechanical properties of a solid, but shows microscopic structural disorder,. A comprehensive understanding of the glassy state is, however, still lacking. A widespread assumption is that the non-exponential relaxation processes observed in the dynamics of glasses — and also in protein dynamics, protein folding and population dynamics — are (in common with other manifestations of complex dynamics) strongly influenced by the underlying energy landscape associated with the structural configurations that the system may adopt. But concrete evidence for this in studies of glass formation has been scarce. Here we present such evidence, obtained from computer simulations of a model glass-forming liquid. We demonstrate that the onset of non-exponential relaxation corresponds to a well defined temperature below which the depth of the potential-energy minima explored by the liquid increases with decreasing temperature, and above which it does not. At lower temperatures, we observe a sharp transition when the liquid gets trapped in the deepest accessible energy basin. This transition temperature depends on the cooling rate, in a manner analogous to the experimental glass transition. We also present evidence that the barrier heights separating potential-energy minima sampled by the liquid increase abruptly at a temperature above the glass transition but well below the onset of non-exponential relaxation. This identification of a relationship between static, topographic features of the energy landscape and complex dynamics holds the promise of a clearer, possibly thermodynamic, understanding of the glass transition.