调节成对势可以控制玻璃形成液体的脆性：从四面体网络到各向同性软球模型
Tuning Pairwise Potential Can Control the Fragility of Glass-Forming Liquids: From Tetrahedral Network to Isotropic Soft Sphere Models
摘要：
我们对Coslovich和Pastore（CP）提出的二氧化硅玻璃成形器模型在广泛的密度范围内进行了分子动力学模拟。密度的变化可以映射到CP模型的Si和O相互作用之间的势深度的变化。通过减小势深（或增加密度），原CP模型中观察到的各向异性四面体网络结构转变为具有纯排斥性软球势的各向同性结构。相应地，弛豫时间的温度依赖性表现出从Arrhenius到超Arrhenius行为的交叉。通过调节单个模型系统的电势，能够在很大范围内控制脆性，这有助于我们弥合网络和各向同性玻璃形成体之间的差距，并深入了解脆性的潜在机制。我们研究了密度关联函数中的Stokes-Einstein破坏的大小和拉伸指数等动力学性质与脆性的关系。我们还表明，比热的峰值系统地移动，随着密度的增加，暗示的脆弱性与系统的隐藏的热力学异常。
英文摘要：
We perform molecular dynamics simulations for a silica glass former model proposed by Coslovich and Pastore (CP) over a wide range of densities. The density variation can be mapped onto the change of the potential depth between Si and O interactions of the CP model. By reducing the potential depth (or increasing the density), the anisotropic tetrahedral network structure observed in the original CP model transforms into the isotropic structure with the purely repulsive soft-sphere potential. Correspondingly, the temperature dependence of the relaxation time exhibits the crossover from the Arrhenius to the super-Arrhenius behavior. Being able to control the fragility over a wide range by tuning the potential of a single model system helps us to bridge the gap between the network and isotropic glass formers and to obtain the insight into the underlying mechanism of the fragility. We study the relationship between the fragility and dynamical properties such as the magnitude of the Stokes-Einstein violation and the stretch exponent in the density correlation function. We also demonstrate that the peak of the specific heat systematically shifts as the density increases, hinting that the fragility is correlated with the hidden thermodynamic anomalies of the system.
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