Shear Modulus and Shear-Stress Fluctuations in Polymer Glasses
I Kriuchevskyi and JP Wittmer and H Meyer and J Baschnagel, PHYSICAL REVIEW LETTERS, 119, 147802 (2017).
Using molecular dynamics simulation of a standard coarse-grained polymer glass model, we investigate by means of the stress-fluctuation formalism the shear modulus mu as a function of temperature T and sampling time Delta t. While the ensemble-averaged modulus mu(T) is found to decrease continuously for all Delta t sampled, its standard deviation delta mu(T) is nonmonotonic, with a striking peak at the glass transition. Confirming the effective time-translational invariance of our systems, mu(Delta t) can be understood using a weighted integral over the shear- stress relaxation modulus G(t). While the crossover of mu(T) gets sharper with an increasing Delta t, the peak of delta mu(T) becomes more singular. It is thus elusive to predict the modulus of a single configuration at the glass transition.
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