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arXiv · 2110.13201

Excess entropy determines the applicability of Stokes-Einstein relation in simple fluids

Sergey Khrapak·Alexey Khrapak
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Abstract

The Stokes-Einstein (SE) relation between the self-diffusion and shear viscosity coefficients operates in sufficiently dense liquids not too far from the liquid-solid phase transition. By considering four simple model systems with very different pairwise interaction potentials (Lennard-Jones, Coulomb, Debye-H\"uckel or screened Coulomb, and the hard sphere limit) we identify where exactly on the respective phase diagrams the SE relation holds. It appears that the reduced excess entropy $s_{\rm ex}$ can be used as a suitable indicator of the validity of the SE relation. In all cases considered the onset of SE relation validity occurs at approximately $s_{\rm ex}\lesssim -2$. In addition, we demonstrate that the line separating gas-like and liquid-like fluid behaviours on the phase diagram is roughly characterized by $s_{\rm ex}\simeq -1$.

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cond-mat.softcond-mat.mtrl-scicond-mat.stat-mechphysics.flu-dynphysics.plasm-ph

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Sergey Khrapak, Alexey Khrapak. 2021-10-25. Excess entropy determines the applicability of Stokes-Einstein relation in simple fluids. https://doi.org/10.1103/physreve.104.044110

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