Invariants in the Yukawa system's thermodynamic phase diagram

TL;DR

This paper demonstrates that the thermodynamic properties of the Yukawa system can be understood through the isomorph theory, revealing invariances in structure and dynamics along specific curves, and extends the theory's applicability to colloidal suspensions and dusty plasmas.

Contribution

It applies the isomorph theory to the Yukawa system, identifying isomorphs analytically and numerically, and confirms invariance of key properties, thus broadening the theory's scope.

Findings

Yukawa system exhibits strong virial potential-energy correlations.

Identified isomorphs using two different methods with close agreement.

Confirmed invariance of structure and dynamics along isomorphs.

Abstract

This paper shows that several known properties of the Yukawa system can be derived from the isomorph theory, which applies to any system that has strong correlations between its virial and potential-energy equilibrium fluctuations. Such "Roskilde-simple" systems have a simplified thermodynamic phase diagram deriving from the fact that they have curves (isomorphs) along which structure and dynamics in reduced units are invariant to a good approximation. We show that the Yukawa system has strong virial potential-energy correlations and identify its isomorphs by two different methods. One method, the so-called direct isomorph check, identifies isomorphs numerically from jumps of relatively small density changes (here 10%). The second method identifies isomorphs analytically from the pair potential. The curves obtained by the two methods are close to each other; these curves are confirmed to be isomorphs by demonstrating the invariance of the radial distribution function, the static structure factor, the mean-square displacement as a function of time, and the incoherent intermediate scattering function. Since the melting line is predicted to be an isomorph, the theory provides a derivation of a known approximate analytical expression for this line in the temperature-density phase diagram. The paper's results give the first demonstration that the isomorph theory can be applied to systems like dense colloidal suspensions and strongly coupled dusty plasmas.