Institut Charles Sadron, Université de Strasbourg & CNRS, 23 rue du Loess, 67034 Strasbourg Cedex, France.
LAMCOS, INSA, 27 av. Jean Capelle, 69621 Villeurbanne Cedex, France.
Phys Rev E. 2018 Jan;97(1-1):012502. doi: 10.1103/PhysRevE.97.012502.
We investigate by means of molecular dynamics simulation a coarse-grained polymer glass model focusing on (quasistatic and dynamical) shear-stress fluctuations as a function of temperature T and sampling time Δt. The linear response is characterized using (ensemble-averaged) expectation values of the contributions (time averaged for each shear plane) to the stress-fluctuation relation μ_{sf} for the shear modulus and the shear-stress relaxation modulus G(t). Using 100 independent configurations, we pay attention to the respective standard deviations. While the ensemble-averaged modulus μ_{sf}(T) decreases continuously with increasing T for all Δt sampled, its standard deviation δμ_{sf}(T) is nonmonotonic with a striking peak at the glass transition. The question of whether the shear modulus is continuous or has a jump singularity at the glass transition is thus ill posed. Confirming the effective time-translational invariance of our systems, the Δt dependence of μ_{sf} and related quantities can be understood using a weighted integral over G(t).
我们通过分子动力学模拟研究了一个粗粒聚合物玻璃模型，重点关注（准静态和动态）剪切应力波动作为温度 T 和采样时间Δt 的函数。线性响应使用（系综平均）对剪切模量和剪切应力弛豫模量 G(t)的应力波动关系 μsf 的贡献（每个剪切平面的时间平均）的期望值来表征。使用 100 个独立的构型，我们注意到各自的标准偏差。虽然对于所有采样的Δt，系综平均模量 μsf(T)随 T 的增加连续减小，但它的标准偏差 δμsf(T)具有非单调特性，在玻璃转变处有一个显著的峰值。因此，剪切模量在玻璃转变处是否连续或具有跳跃奇点的问题是不合适的。通过确认我们系统的有效时间平移不变性，μsf 和相关量的Δt 依赖性可以使用 G(t)的加权积分来理解。
