Fickian yet non-Gaussian diffusion in two-dimensional Yukawa liquids

TL;DR

This study reveals that 2D Yukawa liquids exhibit Fickian diffusion with non-Gaussian features at intermediate times, especially at lower temperatures, due to heterogeneous particle dynamics, challenging the Gaussian approximation assumption.

Contribution

It demonstrates the failure of the Gaussian approximation in describing diffusion in 2D Yukawa liquids and links non-Gaussian behavior to heterogeneous dynamics.

Findings

Deviations from Gaussian behavior increase at lower temperatures.

Non-Gaussian parameter quantifies the deviations.

Heterogeneous dynamics likely cause non-Gaussian diffusion.

Abstract

We investigate Fickian diffusion in two-dimensional (2D) Yukawa liquids using molecular dynamics simulations. We compute the self-van Hove correlation function $G_s(r,t)$, and the self-intermediate scattering function $F_s(k,t)$ and compare these functions with those obtained from mean-squared displacement MSD using the Gaussian approximation. According to this approximation, a linear MSD with time implies a Gaussian behavior for $G_s(r,t)$ and $F_s(k,t)$ at all times. Surprisingly, we find that these functions deviate from Gaussian at intermediate time scales, indicating the failure of the Gaussian approximation. Furthermore, we quantify these deviations by the non-Gaussian parameter, and we find that the deviations increase with decreasing the temperature of the liquid. The origin of the non-Gaussian behavior may be the heterogeneous dynamics of dust particles observed in 2D Yukawa liquids.