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Unveiling the complex glassy dynamics of square shoulder systems: Simulations and theory
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Image of FIG. 1.
FIG. 1.

Square shoulder potential for a generic additive binary mixture of species i, j. Here, σ ij = (1/2)(σ i + σ j ) are the hardcores, Δσ ij are the shoulder widths, and u 0 = 1 is the shoulder height.

Image of FIG. 2.
FIG. 2.

Normalized diffusion coefficient D A /D 0 as a function of (a) ϕ for several isotherms, as reported in the labels. At all investigated T data show a monotonic decrease with increasing ϕ, which clearly indicates the absence of diffusion anomalies associated with compression/expansion. A crossing of the data at high ϕ however signals the presence of a diffusivity maximum associated with cooling; (b) T for several isochores, as reported in the labels.

Image of FIG. 3.
FIG. 3.

(a) Isodiffusivity lines for D A /D 0 = 1.0 × 10−3, 1.0 × 10−4, and 1.1 × 10−5, as well as the extrapolated arrest (D A = 0) lines from the fits D A ∼ |ϕ − ϕ g (T)|γ(T) along isotherms and D A ∼ |TT g ϕ|γ(ϕ) along isochores. The data display a reentrance in T (inset), while no reentrance in ϕ is observed; (b) Power law fits along isotherms (left) and isochores (right).

Image of FIG. 4.
FIG. 4.

Static structure factors for a monodisperse SS system at T = 0.5, ϕ = 0.45 calculated by MD simulations as well as solving the Ornstein-Zernike equation within Rogers-Young (RY) and Percus-Yevick (PY) closures. (Inset) MCT results for the liquid-glass and glass-glass lines using PY and RY.

Image of FIG. 5.
FIG. 5.

MCT results for the binary mixture under study using the static structure factors calculated from simulations as input, labeled as liquid glass (filled squares) and glass-glass (open squares). Arrest curve drawn from ϕ g (filled circles) and T g (filled diamonds) obtained from power-law fits of D A as in Fig. 3 . Mapped MCT lines onto the arrest curve: liquid-glass (filled triangles) and glass-glass (open triangles). Stars are the two predicted higher order singularities and .

Image of FIG. 6.
FIG. 6.

MSD for a particles as a function of scaled time tD 0 for ϕ = 0.525 as a function of T, indicated in the labels. The vertical dotted lines indicate as guides to the eye the regime of subdiffusive behaviour, which is highlighted by the dashed line (∝ t 0.5).

Image of FIG. 7.
FIG. 7.

The density autocorrelation functions for ϕ = 0.525 as a function of time for (a) several wave vectors at T = 0.375. From top to bottom, qσ AA = 1.88, 2.81, 4.68, 5.63, 7.5, 10.32, 13.12, 17.82, 28.13. A concave-convex shape transition is observed around q AA ≈ 7.0, where the decay of is almost purely logarithmic; (b) several T at fixed wave vector q = q*. From left to right, temperatures are T = 1.0, 0.6, 0.5, 0.4, 0.375, 0.35, 0.3, 0.29.

Image of FIG. 8.
FIG. 8.

Critical non-ergodicity parameters for the A species calculated within MCT along the liquid-glass (curves labeled from 1 to 5) and along the glass-glass (curves labeled from 6 to 8) lines. The corresponding state points and their position on the MCT lines are reported in the inset: a non-monotonic behaviour with increasing ϕ is observed for both sets of data.

Image of FIG. 9.
FIG. 9.

(a): Non-ergodicity parameters obtained from simulations, fitting the density auto-correlation functions with stretched exponentials, for the state points reported in the upper inset. The behaviour along the liquid-glass line is strikingly similar to that of MCT predictions, reported in Fig. 8 . (Lower inset) for low ϕ (and low T) (state point 1) is identical to that of high ϕ (state point 6) upon a rescaling by the effective diameter σ + Δ; (b) Stretching exponents β AA obtained from the fits as a function of wave vector for the same state points considered in (a).


Generic image for table
Table I.

Extrapolated values of γ(T), ϕ g , γ(ϕ), and T g obtained from fitting data of Figs. 3(a) and 3(b) with MCT predictions of Eqs. (3) and (4) for the diffusion coefficient D A . Error bars of the fit parameters typically amount to a few percent for the values of ϕ g and T g , while the γ exponents can vary systematically over different fit intervals, so they should be taken with caution.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Unveiling the complex glassy dynamics of square shoulder systems: Simulations and theory