The cosine law at the atomic scale: Toward realistic simulations of Knudsen diffusion

TL;DR

This paper investigates atomic-scale Knudsen diffusion using molecular dynamics, revealing the asymptotic cosine law of reflection, correlations in reflection events, and angle-dependent moments of the reflection process.

Contribution

It introduces a dynamical perspective on the cosine law at the atomic scale and analyzes reflection correlations and angle-dependent moments in Knudsen diffusion.

Findings

Asymptotic cosine law of reflection at atomic scale

Strong correlations in reflection events

Reflection moments depend on incident angle

Abstract

We propose to revisit the diffusion of atoms in the Knudsen regime in terms of a complex dynamical reflection process. By means of molecular dynamics simulation we emphasize the asymptotic nature of the cosine law of reflection at the atomic scale, and carefully analyze the resulting strong correlations in the reflection events. A dynamical interpretation of the accomodation coefficient associated to the slip at the wall interface is also proposed. Finally, we show that the first two moments of the stochastic process of reflection non uniformly depend on the incident angle.