slip length in rough channels

Hi Guys

I simulate a nanochannel with rectangular roughnesses.I wanna calculate slip length at solid-liquid interface.

As you all know in MD simulations we have fluctuations in velocity profile so to calculate slip length, should I calculate velocity slip and velocity gradient at first bin of fluid near wall?

Can I use velocity profile which has been curve fitted? or using velocity profile with fluctuations?(then how to calculate slip length at such diagram)

There are two approaches to measure slip lengths:

* using non equilibrium MD, by imposing a flow (usually a simple
Couette flow) and fitting the whole velocity profile to an analytical
expression taking liquid/solid slip into account. See for instance the
user script "DPD thermostated liquid of LJ chains sheared between
(111) fcc walls" on lammps web page:
http://lammps.sandia.gov/scripts.html
Of course the velocity profiles must be averaged over time to minimize
the effect of thermal fluctuations.

* using equilibrium MD: the slip length is inversely proportional to
the interfacial friction coefficient, which can be computed with a
Green-Kubo formula from the equilibrium fluctuations of the friction
force. For more details, see for instance:
http://dx.doi.org/10.1021/nl1021046

Best,
Laurent

2012/2/26 omid atlaschian <[email protected]>: