**Equilibrium molecular dynamics evaluation of the solid-liquid friction
coefficient: Role of timescales**

H Oga and T Omori and L Joly and Y Yamaguchi, JOURNAL OF CHEMICAL PHYSICS, 159, 024701 (2023).

DOI: 10.1063/5.0155628

Solid-liquid friction plays a key role in nanofluidic systems. Following
the pioneering work of Bocquet and Barrat, who proposed to extract the
friction coefficient (FC) from the plateau of the Green-Kubo (GK)
integral of the solid-liquid shear force autocorrelation, the so-called
plateau problem has been identified when applying the method to finite-
sized molecular dynamics simulations, e.g., with a liquid confined
between parallel solid walls. A variety of approaches have been
developed to overcome this problem. Here, we propose another method that
is easy to implement, makes no assumptions about the time dependence of
the friction kernel, does not require the hydrodynamic system width as
an input, and is applicable to a wide range of interfaces. In this
method, the FC is evaluated by fitting the GK integral for the timescale
range where it slowly decays with time. The fitting function was derived
based on an analytical solution of the hydrodynamics equations **Oga et
al., Phys. Rev. Res. 3, L032019 (2021)**, assuming that the timescales
related to the friction kernel and the bulk viscous dissipation can be
separated. By comparing the results with those of other GK-based methods
and non-equilibrium molecular dynamics, we show that the FC is extracted
with excellent accuracy by the present method, even in wettability
regimes where other GK-based methods suffer from the plateau problem.
Finally, the method is also applicable to grooved solid walls, where the
GK integral displays complex behavior at short times.

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