Spatial correlations of elementary relaxation events in glass-forming liquids

Abstract

The dynamical facilitation scenario, by which localized relaxation events promote nearby relaxation events in an avalanching process, has been suggested as the key mechanism connecting the microscopic and the macroscopic dynamics of structural glasses. Here we investigate the statistical features of this process via the numerical simulation of a model structural glass. First we show that the relaxation dynamics of the system occurs through particle jumps that are irreversible, and that cannot be decomposed in smaller irreversible events. Then we show that each jump does actually trigger an avalanche. The characteristic of this avalanche change on cooling, suggesting that the relaxation dynamics crossovers from a noise dominated regime where jumps do not trigger other relaxation events, to a regime dominated by the facilitation process, where a jump trigger more relaxation events.

Diffusion dynamics of supercooled water modeled with the cage-jump motion and hydrogen-bond rearrangement

“…In this paper, we have developed a cage-jump model for the diffusion in supercooled water. Unlike the scheme proposed by Pastore et al, [26][27][28][29][30][31] we classify the trajectory of a single water molecule into the caged and jumping states from the analysis of H-bond rearrangements. The quantification of the average length and time scales of the jumping state enabled to predict the self-diffusion constant D that is determined in principle from the longtime MSD behavior.…”

Cage-jump motion reveals universal dynamics and non-universal structural features in glass forming liquids

“…The CTRW approach completely neglects the presence of spatial correlations between jumps of dif-ferent particles. Indeed, we recently showed that, for the model considered here, jumps actually occur in group of few particles 28 . Moreover, for a correct CTRW description it is crucial to fairly identify elementary irreversible events.…”

“…In both panels the temperature is T = 2.5, 2.2, 2.0, 1.9, 1.8, and 1.7 × 10 −3 , from left to right. and t p firstly decouples marks the beginning of the Stokes-Einstein (SE) breakdown at the wavelength of the jump length 28 , and, is akin of the onset temperature 39 . Finally, the spatial features of the CTRW approach are fixed by the mean square jump length, ∆r J which decreases on cooling as illustrated in Fig.…”

Relaxation functions and dynamical heterogeneities in a model of chemical gel interfering with glass transition

“…is the average over the bond configurations, and the sums are done on all particles. Three different relaxation time scales are recognised [19] in the relaxation functions: τ β , due to the rattling of particles in cage formed by the neighbors [26,27,28]; τ α > τ β , due to the opening of the cage, diverging at the glass transition line; and finally τ perc > τ α , due to the relaxation of the largest cluster, diverging at the gel transition line (see Fig. 2a).…”