Intermolecular distance and density scaling of dynamics in molecular liquids

TL;DR

This paper investigates how the dynamics of molecular liquids scale with intermolecular distance and density, revealing that the scaling exponent depends on molecular structure rather than the interatomic potential.

Contribution

It introduces a new relation for the density scaling exponent in molecular liquids, linking it to molecular structure through the parameter {\delta}.

Findings

The scaling exponent {\gamma} equals n/{\delta} in molecular liquids.

{\delta} depends solely on molecular structure, not on the interatomic potential.

Density scaling applies broadly to molecular liquids with rigid bonds.

Abstract

A broad variety of liquids conform to density scaling: relaxation times expressed as a function of the ratio of temperature to density, the latter raised to a material constant {\gamma}. For atomic liquids interacting only through simple pair potentials, the exponent {\gamma} is very nearly equal to n/3, where n is the steepness of the intermolecular potential, while for molecular liquids having rigid bonds and built using the same interatomic potential, {\gamma}>n/3. We find that for this class of molecular liquids {\gamma}=n/{\delta}, where the parameter {\delta} relates the intermolecular distance to the density along an isomorph (line of approximately constant dynamics and structure). {\delta} depends only on the molecular structure and not the interatomic potential.