"Isomorphs" in liquid state diagrams

TL;DR

This paper introduces the concept of isomorphic lines in the phase diagram of strongly correlating liquids, showing they share key properties and can be scaled into a master isomorph, based on computer simulations of Lennard-Jones liquids.

Contribution

It defines isomorphs in strongly correlating liquids and demonstrates their properties and universal scaling behavior through simulations and theoretical derivations.

Findings

Isomorphic points have identical excess entropy and reduced relaxation times.

No aging occurs when jumping between isomorphic points.

All Lennard-Jones 12-6 liquids share the same scaled isomorphs.

Abstract

A liquid is termed strongly correlating if its virial and potential energy thermal equilibrium fluctuations in the NVT ensemble are more than 90% correlated [Phys. Rev. Lett. 100, 015701 (2008)]. The fluctuations of a strongly correlating liquid are well approximated by those of an inverse power-law intermolecular potential. Building on this fact we here define "isomorphic lines" in the state diagram of a strongly correlating liquid. It is shown from computer simulations of the Kob-Andersen binary Lennard-Jones liquid that no aging is associated with jumps between two isomorphic points. Isomorphic state points have the same excess entropy, the same reduced average relaxation time, the same (reduced) dynamics, and the same scaled radial distribution functions. Finally we calculate the equation for isomorphs in the virial / potential energy diagram for Lennard-Jones type liquids and show that all such 12-6 liquids have the same isomorphs; these may be scaled into a master isomorph.