Microscopic Origin of Shear Relaxation in Strongly Coupled Yukawa Liquids

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 (${\tau }_M^{id},{\tau }_M^{ex},{\tau }_M$ respectively) along with the lifetime of local atomic connectivity ${\tau }_{LC}$ leads us to the following important observation. Below a certain crossover ${\Gamma }_c(\kappa )$, ${\tau }_{LC}\to {\tau }_M^{ex}$, 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, ${\tau }_M^{ex}\to {\tau }_M$ meaning that ${\tau }_M^{ex}$ can fully account for the elastic or "solid like" behavior.

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