Microscopic Origin of Shear Relaxation in Strongly Coupled Yukawa Liquids

TL;DR

This study uses molecular dynamics to explore how shear stress relaxes in strongly coupled Yukawa liquids, revealing a crossover point where local atomic connectivity governs excess shear stress relaxation, transitioning from microscopic to collective behavior.

Contribution

It identifies the microscopic origin of shear stress relaxation in Yukawa liquids and characterizes the crossover behavior based on coupling strength and screening parameters.

Findings

Below a critical coupling, local atomic connectivity determines excess shear stress relaxation.

At high coupling, excess shear stress relaxation accounts for elastic, solid-like behavior.

The crossover coupling strength depends on the screening parameter .

Abstract

We report accurate molecular dynamics calculations of the shear stress relaxation in a two-dimensional strongly coupled Yukawa liquid over a wide range of the Coulomb coupling strength $\Gamma$ and the Debye screening parameter $\kappa$. Our data on the relaxation times of the ideal- , excess- and total shear stress auto-correlation ($\tau^{id}_M, \tau^{ex}_M, \tau_M$ respectively) along with the lifetime of local atomic connectivity $\tau_{LC}$ leads us to the following important observation. Below a certain crossover $\Gamma_c(\kappa)$, $\tau_{LC} \rightarrow \tau^{ex}_M$, directly implying that here $\tau_{LC}$ is the microscopic origin of the relaxation of excess shear stress unlike the case for ordinary liquids where it is the origin of the relaxation of the total shear stress. At $\Gamma >> \Gamma_c(\kappa)$ i.e. in the potential energy dominated regime, $\tau^{ex}_M\rightarrow \tau_M$ meaning that $\tau^{ex}_M$ can fully account for the elastic or "solid like" behavior.