Equation of state in the generalized density scaling regime studied from ambient to ultra-high pressure conditions

Abstract

In this paper, based on the effective intermolecular potential with well separated density and configuration contributions and the definition of the isothermal bulk modulus, we derive two similar equations of state dedicated to describe volumetric data of supercooled liquids studied in the extremely wide pressure range related to the extremely wide density range. Both the equations comply with the generalized density scaling law of molecular dynamics versus $h(\rho )/T$ at different densities $\rho$ and temperatures $T$, where the scaling exponent can be in general only a density function $\gamma (\rho )=d\ln h/d\ln \rho$ as recently argued by the theory of isomorphs. We successfully verify these equations of state by using data obtained from molecular dynamics simulations of the Kob-Andersen binary Lennard-Jones liquid. As a very important result, we find that the one-parameter density function $h(\rho )$ analytically formulated in the case of this prototypical model of supercooled liquid, which implies the one-parameter density function $\gamma (\rho )$, is able to scale the structural relaxation times with the value of this function parameter determined by fitting the volumetric simulation data to the equations of state. We also show that these equations of state properly describe the pressure dependences of the isothermal bulk modulus and the configurational isothermal bulk modulus in the extremely wide pressure range investigated by the computer simulations. Moreover, we discuss the possible forms of the density functions $h(\rho )$ and $\gamma (\rho )$ for real glass formers, which are suggested to be different from those valid for the model of supercooled liquid based on the Lennard-Jones intermolecular potential.

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