Bulk viscosity of the Lennard-Jones system at the triple point by dynamical Non Equilibrium Molecular Dynamics

TL;DR

This study uses dynamical NEMD to accurately determine the bulk viscosity of Lennard-Jones fluid at the triple point, resolving previous discrepancies with Green-Kubo estimates and confirming Newtonian behavior.

Contribution

It demonstrates that careful application of the dynamical NEMD method and specific techniques yields bulk viscosity estimates in agreement with Green-Kubo results, clarifying prior disagreements.

Findings

NEMD estimates match Green-Kubo values when using the proper techniques.

Bulk viscosity shows a large linear response regime at the triple point.

Lennard-Jones fluid behaves as a Newtonian fluid at the triple point.

Abstract

Non-equilibrium Molecular Dynamics (NEMD) calculations of the bulk viscosity of the triple point Lennard-Jones fluid are performed with the aim of investigating the origin of the observed disagreement between Green-Kubo estimates and previous NEMD data. We show that a careful application of the Doll's perturbation field, the dynamical NEMD method, the instantaneous form of the perturbation and the "subtraction technique" provides a NEMD estimate of the bulk viscosity at zero field in full agreement with the value obtained by the Green-Kubo formula. As previously reported for the shear viscosity, we find that the bulk viscosity exhibits a large linear regime with the field intensity which confirms the Lennard-Jones fluid as a genuine Newtonian fluid even at triple point.