Hidden scale invariance in molecular van der Waals liquids: A simulation study

TL;DR

This study uses molecular dynamics simulations to reveal a hidden approximate scale invariance in van der Waals liquids, where equilibrium potential energy fluctuations and structural properties follow inverse power law scaling, but the equation of state does not.

Contribution

The paper demonstrates that van der Waals liquids exhibit a hidden scale invariance characterized by inverse power law behavior in potential energy fluctuations and structural properties, expanding understanding of liquid dynamics.

Findings

Potential energy fluctuations follow inverse power law scaling.

Radial distribution functions obey IPL scaling properties.

Equation of state does not follow IPL scaling.

Abstract

Results from molecular dynamics simulations of two viscous molecular model liquids -- the Lewis-Wahnstrom model of ortho-terphenyl and an asymmetric dumbbell model -- are reported. We demonstrate that the liquids have a ``hidden'' approximate scale invariance: Equilibrium potential energy fluctuations are accurately described by inverse power law (IPL) potentials, the radial distribution functions are accurately reproduced by the IPL's, and the radial distribution functions obey the IPL predicted scaling properties to a good approximation. IPL scaling of the dynamics also applies -- with the scaling exponent predicted by the equilibrium fluctuations. In contrast, the equation of state does not obey the IPL scaling. We argue that our results are general for van der Waals liquids, but do not apply, e.g., for hydrogen-bonded liquids.