"Pseudoisomorphs" in liquids with intramolecular degrees of freedom

TL;DR

This paper demonstrates that liquids with harmonic intramolecular bonds exhibit pseudoisomorphic lines of invariant dynamics, explained through scale invariance of vibrational spectra, elucidating the applicability of various scaling laws.

Contribution

It introduces a method to identify pseudoisomorphic lines in liquids with internal degrees of freedom based on vibrational spectrum scale invariance.

Findings

Pseudoisomorphic lines exist in liquids with harmonic intramolecular bonds.

Invariance of vibrational spectra characterizes these lines.

This explains the success of excess-entropy and density scaling laws.

Abstract

Computer simulations show that liquids of molecules with harmonic intramolecular bonds may have "pseudoisomorphic" lines of approximately invariant dynamics in the thermodynamic phase diagram. We demonstrate that these lines can be identified by requiring scale invariance of the inherent-structure reduced-unit low-frequency vibrational spectrum evaluated for a single equilibrium configuration. This rationalizes why excess-entropy scaling, density scaling, and isochronal superposition apply for many liquids with internal degrees of freedom.