Entropy, local order, and the freezing transition in Morse liquids

Abstract

The behavior of the excess entropy of Morse and Lennard-Jones liquids is examined as a function of temperature, density, and the structural order metrics. The dominant pair correlation contribution to the excess entropy is estimated from simulation data for the radial distribution function. The pair correlation entropy (S2) of these simple liquids is shown to have a threshold value of (-3.5+/-0.3)kB at freezing. Moreover, S2 shows a T(-2/5) temperature dependence. The temperature dependence of the pair correlation entropy as well as the behavior at freezing closely correspond to earlier predictions, based on density functional theory, for the excess entropy of repulsive inverse power and Yukawa potentials [Rosenfeld, Phys. Rev. E 62, 7524 (2000)]. The correlation between the pair correlation entropy and the local translational and bond orientational order parameters is examined, and, in the case of the bond orientational order, is shown to be sensitive to the definition of the nearest neighbors. The order map between translational and bond orientational order for Morse liquids and solids shows a very similar pattern to that seen in Lennard-Jones-type systems.

Triplet Correlations Dominate the Transition from Simple to Tetrahedral Liquids

“…The λ ¼ 16 liquid satisfies the T −2=5 scaling over the temperature range from T ¼ 0.18 to T thr ¼ 0.035, where T thr represents the threshold temperature below which the liquid crystallizes during the simulation run [36]. The values of S e at T m and T thr are −4.7k B and −5.4k B , respectively, consistent with results for other simple liquids [3,[42][43][44][45][46]. The total isobaric heat capacity, C p , shows a small rise on supercooling from 3.5k B to 4k B .…”

Isomorphs, hidden scale invariance, and quasiuniversality

“…• Quasiuniversality of the translational/orientational order-parameter maps of Debenedetti and coworkers [63][64][65].…”

Determining landscape-based criteria for freezing of liquids

“…The simulations in the solid phase were initiated at a low temperature ͑T = 0.1͒ with an ordered face-centered cubic ͑fcc͒ structure. 13,14 From the Monte Carlo runs for the 256-particle SLJ system, a set of 800 and 200 instantaneous configurations was sampled at equispaced intervals and used to initiate isochoric quenches to locate inherent structures and inherent saddles, respectively, corresponding to local minimizations of the potential energy U͑r͒ and the gradient-squared function W͑r͒ = ٌ͉U͉ 2 , respectively. 49 Along each isobar, the simulation temperatures were gradually in- creased until the superheated solid spontaneously melted.…”

“…[12][13][14] The relationship of S e to the calorimetric entropy is obvious. As a dimensionless quantity, it can serve as a good variable to monitor either temperature-or pressure-driven freezing process.…”