On the equilibrium calculation of the friction coefficient for liquid slip against a wall.

We demonstrate that the linear response theory of interface friction presented by Bocquet and Barrat [Phys. Rev. E 49, 3079 (1994)] results in a friction coefficient that is not an intrinsic property of the interface and thus does not correspond to the actual interfacial friction coefficient. We point out that this previous derivation includes an unsubstantiated identification of the velocity field in the nonuniform system with the perturbation applied to the equations of the motion. We present an alternative equilibrium theory of the friction associated with the confined fluid and show how this friction is related to the intrinsic interfacial friction.