Brownian motion from molecular dynamics

TL;DR

This study uses molecular dynamics simulations to analyze Brownian motion, focusing on how particle mass and size influence the fluctuating forces and memory effects in different fluid densities.

Contribution

It provides detailed insights into the fluctuating force distributions and memory functions for particles of various sizes and masses, extending understanding of Brownian dynamics.

Findings

Fluctuating force distribution deviates from Gaussian for small diameters.

Deviations decrease linearly with mass ratio for heavy particles.

Memory functions depend on particle size, mass, and fluid density.

Abstract

Brownian motion of single particles with various masses M and diameters D is studied by molecular dynamics simulations. Besides the momentum auto-correlation function of the Brownian particle the memory function and the fluctuating force which enter the generalized Langevin equation of the Brownian particle are determined and their dependence on mass and diameter are investigated for two different fluid densities. Deviations of the fluctuating force distribution from a Gaussian form are observed for small particle diameters. For heavy particles the deviations of the fluctuating force from the total force acting on the Brownian particle decrease linearly with the mass ratio m/M where m denotes the mass of a fluid particle.