Unifying reciprocal and real space atomic dynamics in dilute gases

TL;DR

This paper demonstrates that normal modes, traditionally associated with solids, can be used to describe atomic dynamics and transport processes in dilute gases, bridging the gap between solid and gas phase theories.

Contribution

It introduces a unifying framework using normal modes to describe atomic dynamics in dilute gases, extending their applicability beyond crystalline solids.

Findings

Normal modes can describe transport processes in dilute gases.

Normal modes unify solid and gas phase atomic dynamics.

Results are demonstrated on argon gas.

Abstract

In solids, quanta of atomic vibrations are identified in reciprocal space by their frequency and wavevector as phonons. At the opposite end of the matter spectrum, dynamics of dilute gases is conventionally described in terms of atomic or molecular collisions and translations in real space and time. These two formalisms are apparently incompatible, leading to difficulties in understanding atomic dynamics in intermediate matter. In this work, we demonstrate that normal modes, often synonymously considered as phonons in solids, provide a microscopic description of various transport processes, including thermal conductivity, diffusion coefficient, and shear viscosity, in a prototypical dilute gas, argon. Our results bridge the conceptual divide between solid and gas phase descriptions and establish normal modes as a unifying framework for atomic dynamics well beyond crystalline solids.