Evidence of short time dynamical correlations in simple liquids

TL;DR

This study uses molecular dynamics simulations to reveal that short-time particle motions in simple liquids are strongly correlated and exhibit a fast relaxation process similar to that in glasses, persisting well above melting points.

Contribution

It demonstrates the presence of a persistent, fast relaxation process in simple liquids, challenging the assumption of uncorrelated binary collisions at high temperatures.

Findings

Fast relaxation process exists in both glassy and liquid phases.

The relaxation parameters show almost no temperature dependence.

Short-time particle motions are strongly correlated even above melting point.

Abstract

We report a molecular dynamics (MD) study of the collective dynamics of a simple monatomic liquid -interacting through a two body potential that mimics that of lithium- across the liquid-glass transition. In the glassy phase we find evidences of a fast relaxation process similar to that recently found in Lennard-Jones glasses. The origin of this process is ascribed to the topological disorder, i.e. to the dephasing of the different momentum $Q$ Fourier components of the actual normal modes of vibration of the disordered structure. More important, we find that the fast relaxation persists in the liquid phase with almost no temperature dependence of its characteristic parameters (strength and relaxation time). We conclude, therefore, that in the liquid phase well above the melting point, at variance with the usual assumption of {\it un-correlated} binary collisions, the short time particles motion is strongly {\it correlated} and can be described via a normal mode expansion of the atomic dynamics.