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Updated: Aug 7, 2026

Impacts of Free-falling Spheres on a Deep Liquid Pool with Altered Fluid and Impactor Surface Conditions
Published on: February 17, 2019
Nature of the breakdown in the Stokes-Einstein relationship in a hard sphere fluid
Sanat K Kumar1, Grzegorz Szamel, Jack F Douglas
1Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA. kumar@rpi.edu
Abstract:
Molecular dynamics simulations of high density hard sphere fluids clearly show a breakdown of the Stokes-Einstein equation (SE). This result has been conjectured to be due to the presence of mobile particles, i.e., ones which have the propensity to "hop" distances that are integer multiples of the interparticle distance. We conclusively show that the sedentary particles, i.e., ones complementary to the "hoppers," obey the SE relationship to a good approximation, even though the fluid as a whole violates the SE equation at high densities. These results support the notion that the unusual diffusive behavior of supercooled liquids is dominated by the hopping particles.
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