On the relaxation dynamics of glass-forming systems: Insights from computer simulations

Abstract

Abstract. We discuss the relaxation dynamics of a simple lattice gas model for glass-forming systems and show that with increasing density of particles this dynamics slows down very quickly. By monitoring the trajectory of tagged particles we find that their motion is very heterogeneous in space and time, leading to regions in space in which there is a fast dynamics and others in which it is slow. We determine how the geometric properties of these quickly relaxing regions depend on density and time. Motivated by this heterogeneous hopping dynamics, we use a simple model, a variant of a continuous time random walk, to characterize the relaxation dynamics. In particular we find from this model that for large displacements the self part of the van Hove function shows an exponential tail, in agreement with recent findings from experiments and simulations of glassforming systems.

The jamming scenario—an introduction and outlook

“…Such states have higher values of φ c , since the potential energy increases with φ−φ c . Thus, the average value of φ c for the ensemble must increase as the system is quenched from lower temperatures, in accordance with the results of Chaudhuri, et al [9], and the system can be described as having a line of jamming transitions extending upwards from φ ≈ 0.64, as in Ref. [10].…”

“…In that case, φ c ≈ 0.64 for monodisperse spheres in three dimensions [5]. However, if the ensemble is prepared by a quench from a system equilibrated at a low temperature, the onset packing fraction is higher [8,9]. It is clear from the distribution of jamming onsets that this must be the case [5].…”

From crystal to amorphous: A novel route to unjamming in soft disk packings

“…It has been extensively studied recently both by simula-tions [1,2,3,4,5,6,7,8,9,10] and experiments [11,12]. As expected for strongly interacting systems, there are several theoretical proposals [13,14,15,16] to describe this state, most of them relying on approximate mean-field arguments.…”

“…It prevents any crystallization that may occur during a slow rearrangement of particle positions during equilibration. Second, the critical jamming density is affected by particle size ratio [10], shape [17] and the preparation protocol, but its critical properties are the same (recently, Chaudhuri et al [9] showed that this critical point is not unique, even for large systems). Third, the jamming point in monodisperse and bidisperse packings is manifested in structural properties as the δ-function behavior of the first peak of the radial distribution function and the split of its second neighbor peak [7].…”

Local dynamical heterogeneity in glass formers

“…The riddle is vividly illustrated by the strong growth around the glass transition of a simple single-particle observable that quantifies the non-Gaussian character of displacement fluctuations, the long-studied non-Gaussian parameter α 2 (t) [19]. A possible explanation for this growth is that in the supercooled regime, at intermediate times different populations of particles -fast and slow-emerge; both display normal diffusion but their superposed behavior leads to an apparent non-Gaussianity [20]. Yet the remarkable similarity between both the time evolution and the temperature dependence of α 2 and those of χ 4 suggest that growing particle-level fluctuations might then also play a role.…”