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Updated: May 8, 2026

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids
Published on: December 4, 2017
Gaussian field theory for the Brownian motion of a solvated particle
1Institut für Theoretische Physik II, Heinrich-Heine-Universität Düsseldorf, Universitätsstrasse 1, 40225 Düsseldorf, Germany.
Abstract:
An alternative derivation of Brownian motion is presented. Instead of supplementing the linearized Navier-Stokes equations with a fluctuating force, we directly assume a Gaussian action functional for solvent velocity fluctuations. Solvating a particle amounts to expelling the solvent and prescribing a boundary condition to the solvent on the interface that is shared with the solute. We study the dynamical effects of this boundary condition on the solvent and derive explicit expressions for the solvent mean flow and velocity correlations. Moreover, we show that the probability to observe solvent velocity fluctuations that are compatible with the boundary condition reproduces random Brownian motion of the solvated particle. We explicitly calculate the translational and rotational diffusion coefficients of a spherical particle using the presented formalism.
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