Abstract
We compute partial structure factors, Kirkwood-Buff integrals (KBIs) and chemical potentials of model supercooled liquids with and without attractive interactions. We aim at investigating whether relatively small differences in the tail of the radial distribution functions result in contrasting thermodynamic properties. Our results suggest that the attractive potential favours the nucleation of long-range structures. Indeed, upon decreasing temperature, Bathia-Thornton structure factors display anomalous behaviour in the k→0 limit. KBIs extrapolated to the thermodynamic limit confirm this picture, and excess coordination numbers identify the anomaly with long-range concentration fluctuations. By contrast, the purely repulsive system remains perfectly miscible for the same temperature interval and only reveals qualitatively similar concentration fluctuations in the crystalline state. Furthermore, differences in both isothermal compressibilities and chemical potentials show that thermodynamics is not entirely governed by the short-range repulsive part of the interaction potential, emphasising the nonperturbative role of attractive interactions. Finally, at higher density, where both systems display nearly identical dynamical properties and repulsive interactions become dominant, the anomaly disappears, and both systems also exhibit similar thermodynamic properties.
Highlights
We investigate various thermodynamic properties of KALJ and KAWCA a–b mixtures in the supercooled liquid state
We demonstrate that seemingly small differences in the tail of the radial distribution function result in significantly different structural and thermodynamic properties for supercooled systems with and without attractive interactions
Visual inspection of the radial distribution functions (RDFs) for both systems reveals that they are almost indistinguishable (Fig. S1, Electronic supplementary information (ESI)†), and only the RDF gbb(r) for the minor component shows relatively small differences, visible at r o3s (Fig. 1(a)).[20,44]. This direct comparison is misleading: a few thermodynamic quantities are quite sensitive to small fluctuations in the tail of the RDFs
Summary
The supercooled state challenges our understanding of the theory of liquids. In particular, the connection between dynamics, which varies considerably upon supercooling, and structure, which appears to remain essentially unchanged, is the subject of intense research.[1–7] Model systems with reduced complexity, still retaining essential physical features, provide a direct route to investigate this problem. Kob– Andersen mixtures[8] with purely repulsive Weeks-ChandlerAndersen interactions (KAWCA)[9] exhibit substantially different dynamics compared to their Lennard-Jones counterpart (KALJ).[8] By contrast, their structure, investigated from the point of view of radial distribution functions, is somewhat similar.[7,10]. Deviations in many-body structural descriptors such as triplet[12] and point-to-set correlations,[13] as well as bond-order distributions[14] and the packing capabilities of local particle arrangements,[2] have been observed between the KALJ and KAWCA systems These results indicate that higher-order features may be necessary to resolve the difference in their dynamical properties.[15]. Concerning the comparison between models, Bhattacharyya and coworkers[19,20] directly explored structure-dynamics relationships in KALJ and KAWCA systems They used the Adam–Gibbs relation,[21] to connect relaxation time to the configurational entropy.
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