Structural order as a genuine control parameter of dynamics in simple glass formers

Abstract

Glass transition is characterised by drastic dynamical slowing down upon cooling, accompanied by growing spatial heterogeneity. Its rationalisation by subtle changes in the liquid structure has been long debated but remains elusive, due to intrinsic difficulty in detecting the underlying complex structural ordering. Here we report that structural order parameter characterising local packing capability can well describe the glassy dynamics not only macroscopically but also microscopically, no matter whether it is driven by temperature or density. A Vogel-Fulcher-Tammann (VFT)-like relation is universally identified between the structural relaxation time and the order parameter for supercooled liquids with isotropic interactions. More importantly, we find such an intriguing VFT-like relation to be statistically valid even at a particle level, between spatially coarse-grained structural order and microscopic particle-level dynamics. Such a unified description of glassy dynamics based solely on structural order is expected to contribute to the ultimate understanding of the long-standing glass-transition problem.

Slowing down of dynamics and orientational order preceding crystallization in hard-sphere systems

“…Typically, the relaxation time τ of hard-sphere systems increases with volume fraction while approaching dense-packed states ( 7 – 9 , 41 ), which is experimentally observed for ϕ ≤ 0.545 (region I). This behavior can be described by a Vogel-Fulcher-Tammann (VFT) law ( 7 , 14 , 21 ) with the so-called fragility index D , a VFT volume fraction ϕ VFT , and a scaling time τ 0 . We find D = 0.35, which is in good agreement with previous studies ( 7 ), and ϕ VFT = 0.56.…”

“…A recent simulation study on liquids has shown a nontrivial three-dimensional (3D) structure that has been identified by higher-order correlations ( 20 ). Furthermore, orientational order, such as an interplay of crystal-like and icosahedral order, appears to play a key role in the glass transition ( 7 , 9 , 11 , 14 , 21 ). XCCA can contribute to identify orientational order via higher-order correlations ( 22 , 23 ).…”

Assessing the structural heterogeneity of supercooled liquids through community inference

“…Explicit formulation of the inference problem in terms of partial correlations, see Eq. (21), provides a method to quantify the respective contribution of geometry, local density and composition to structure. The overlap between communities inferred from Eq.…”

“…(18) and Eq. (21). As in previous work on network-theoretic community detection [37], we have used a simple local optimization algorithm to find the maxima of I(k; s).…”

“…The correlation between the spatial fluctuations of dynamics in the isoconfigurational ensemble and local structural descriptors appears, however, systemdependent [17,18]. Recent studies have shown that order parameters quantifying local packing efficiency [19][20][21] are highly predictive of the dynamics in hard (or nearly hard) spheres, but these results do not carry over universally to other models. The spatial distribution of soft modes [22,23] correlates well with the local dynamics, at least on time scales shorter than the structural relaxation time, but normal modes obviously contain richer information than the bare structure, since they account for local variations of the energy function.…”