Relaxation of a steep density gradient in a simple fluid: comparison between atomistic and continuum modeling

TL;DR

This study compares atomistic and continuum models for fluid density relaxation, finding good agreement at larger scales but significant differences at molecular scales, especially in temperature predictions.

Contribution

It provides a detailed comparison between molecular dynamics and continuum simulations for density relaxation, highlighting scale-dependent accuracy and limitations of empirical relations.

Findings

Continuum models match atomistic results for large-scale density profiles.

At molecular scales, continuum fields are smoother and less accurate.

Temperature fields show large discrepancies due to empirical equation of state limitations.

Abstract

We compare dynamical nonequilibrium molecular dynamics and continuum simulations of the dynamics of relaxation of a fluid system characterized by a non uniform density profile. Results match quite well as long as the lengthscale of density nonuniformities are greater than the molecular scale (10 times the molecular size). In presence of molecular scale features some of the continuum fields (e.g. density and momentum) are in good agreement with atomistic counterparts, but are smoother. On the contrary, other fields, such at the temperature field, present very large difference with respect to reference (atomistic) ones. This is due to the limited accuracy of some of the empirical relations used in continuum models, the equation of state of the fluid in the example considered.