Structural correlations and cooperative dynamics in supercooled liquids

Abstract

The relationships between diffusivity and the excess, pair and residual multiparticle contributions to the entropy are examined for Lennard-Jones liquids and binary glassformers, in the context of approximate inverse power law mappings of simple liquids. In the dense liquid where diffusivities are controlled by collisions and cage relaxations, Rosenfeld-type excess entropy scaling of diffusivities is found to hold for both crystallizing as well as vitrifying liquids. The crucial differences between the two categories of liquids emerge only when local cooperative effects in the dynamics result in significant caging effects in the time-dependent behaviour of the single-particle mean square displacement. In the case of glassformers, onset of such local cooperativity coincides with onset of deviations from Rosenfeld-type excess entropy scaling of diffusivities and increasing spatiotemporal heterogeneity. In contrast, for two- and three-dimensional liquids with a propensity to crystallise, the onset of local cooperative dynamics is sufficient to trigger crystallization provided that the liquid is sufficiently supercooled that the free energy barrier to nucleation of the solid phase is negligible. The state points corresponding to onset of transient caging effects can be associated with typical values, within reasonable bounds, of the excess, pair, and residual multiparticle entropy as a consequence of the isomorph-invariant character of the excess entropy, diffusivity and related static and dynamic correlation functions.

Determination of onset temperature from the entropy for fragile to strong liquids

“…They have reported that for the KA model at ρ = 1.2 the plateau appears at T = 0.8. Chakravarty et al have identified the T onset from the onset of the plateau in MSD and for KA model at the same density this has a higher value 43 . We plot q(t) of KA model at ρ = 1.2 for different temperatures in Fig.…”

“…The S ex has been evaluated using the procedure given in Ref- 43 . The entropy was initially evaluated at a high temperature and low reduced density for each model, where the system can be assumed to behave as an ideal gas.…”

Isomorphs, hidden scale invariance, and quasiuniversality

“…• Excess entropy scaling, stating that the reduced-unit diffusion constants of different liquids have an approximately universal dependence on the excess entropy per particle [66][67][68][69].…”

Validity of the Rosenfeld relationship: A comparative study of the network forming NTW model and other simple liquids

“…Recently Coslovich and Pastore have proposed a new model of a simple liquid (NTW model) which mimics the properties like the structure and the dynamics of the network forming liquids 26,27 . Since earlier studies have reported the Rosenfeld behaviour to be different for simple and network forming liquids 7,8 , it will be interestingly to investigate the Rosenfeld scaling of the NTW model.…”

“…A semi-quantitative relation between dynamical properties like diffusivity or relaxation times and the thermodynamics has been proposed by Rosenfeld 1,2 and recently it has been extensively studied for different systems [3][4][5][6][7][8][9] . The relationship suggests that the fluid should follow X * = C exp[−KS ex ], where X * is the dimensionless dynamical quantity and S ex is excess entropy which is the difference between the total thermodynamic entropy (S tot ) and the corresponding ideal gas entropy (S id ) at the same temperature (T ) and density (ρ).…”