**Microscopic Slip Boundary Conditions in Unsteady Fluid Flows**

JA de la Torre and D Duque-Zumajo and D Camargo and P Espanol, PHYSICAL REVIEW LETTERS, 123, 264501 (2019).

DOI: 10.1103/PhysRevLett.123.264501

An algebraic tail in the Green-Kubo integral for the solid-fluid friction coefficient hampers its use in the determination of the slip length. A simple theory for discrete nonlocal hydrodynamics near parallel solid walls with extended friction forces is given. We explain the origin of the algebraic tail and give a solution of the plateau problem in the Green-Kubo expressions. We derive the slip boundary condition with a microscopic expression for the slip length and the hydrodynamic wall position, and assess it through simulations of an unsteady plug flow.

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