Onset of two collective excitations in the transverse dynamics of a simple fluid

Abstract

A thorough analysis of the transverse current autocorrelation function obtained by molecular dynamics simulations of a dense Lennard-Jones fluid reveals that even such a simple system is characterized by a varied dynamical behavior with changing length scale. By using the exponential expansion theory, we provide a full account of the time correlation at wavevectors $Q$ between the upper boundary of the hydrodynamic region and $Q_p/2$, with $Q_p$ the position of the main peak of the static structure factor. In the $Q$ range studied we identify and accurately locate the wavevector at which shear wave propagation starts to take place, and show clearly how this phenomenon may be represented by a damped harmonic oscillator changing, in a continuous way, from an overdamped to an underdamped condition. The decomposition into exponential modes allows one to convincingly establish not only the crossover related to the onset of transverse waves but, surprisingly, also the existence of a second pair of modes equivalent to another oscillator that undergoes, at higher $Q$ values, a similarly smooth over- to underdamped transition.

6 pages and 4 figures in main text, 6 pages and 3 figures in supplementary material

References in corpus (3)

• Emergence and evolution of $k$-gap in spectra of liquid and supercritical states
• Density of states and dynamical crossover in a dense fluid revealed by exponential mode analysis of the velocity autocorrelation function
• Modeling neutron and X-ray scattering by liquids

Cited by in corpus (3)

• Experimental observation of gapped shear waves and liquid-like to gas-like dynamical crossover in active granular matter
• Emergence of Debye scaling in the density of states of liquids under nanoconfinement
• Role of the single-particle dynamics in the transverse current autocorrelation function of a liquid metal