Explaining why simple liquids are quasi-universal

Abstract

It has been known for a long time that many simple liquids have surprisingly similar structure as quantified, for example, by the radial distribution function. A much more recent realization is that the dynamics are also very similar for a number of systems with quite different pair potentials. Systems with such non-trivial similarities are generally referred to as 'quasi-universal'. From the fact that the exponentially repulsive pair potential has strong virial potential-energy correlations in the low-temperature part of its thermodynamic phase diagram, we here show that a liquid is quasi-universal if its pair potential can be written approximately as a sum of exponential terms with numerically large prefactors. Based on evidence from the literature we moreover conjecture the converse, that is, that quasi-universality only applies for systems with this property.

Thermodynamics of Yukawa fluids near the one-component-plasma limit

“…The accuracy of this scaling for various model systems has been recently investigated in extensive numerical simulations [23]. It has been observed that the RT scaling is particulary useful for liquids with strong correlations between equilibrium fluctuations of virial and potential energy [23], which are referred to as Rosklide-simple or just Rosklide systems [24]. OCP and strongly coupled Yukawa systems belong to this class and, thus, RT scaling can be quite useful to describe thermodynamic properties of these systems.…”

Communication: Simple liquids’ high-density viscosity

“…31,44 For such systems, the scaling property is rarely obvious from the mathematical expression for U(R) for which reason the term "hidden scale invariance" is sometimes used. 28,33,[45][46][47][48][49] The R-simple region of a given system is identified in computer simulations as the state points characterized by strong virial potential-energy correlations in constant-volume canonical-ensemble fluctuations. 28,50,51 For the LJ liquid, our simulations have shown that the Pearson correlation coefficient obeys R > 0.94 at all state points with density and temperature higher than those of the liquid at the triple point.…”

Density scaling and quasiuniversality of flow-event statistics for athermal plastic flows

“…A more general scaling is established below based on the concept of "hidden scale invariance" [27]. The second purpose of this paper is to show that by using this novel scaling, which involves no more parameters than the traditional power-law scaling, "quasiuniversality" [57] of the flow-event properties is revealed. By this we mean that in properly scaled units the flow-event statistical properties are (almost) independent of the microscopic interactions.…”

“…We interpret this as reflecting a manifestation of the so-called quasiuniversality that was previously only discussed for equilibrium liquids (see, e.g., Refs. [57,67] and references therein). Thus, it has been known for some time that for simple liquids like inverse-power law systems, LJ systems, etc., the radial distribution functions are virtually indistinguishable [68,69].…”