  A velocity boundary condition for the Lattice Boltzmann simulation technique
has been proposed recently by Hecht and Harting[arxiv:0811.4593]. This boundary
condition is independent of the relaxation process during collision and
contains no artificial slip. In this work, this boundary condition is extended
to simulate slip-flows. The extended boundary condition has been tested and it
is found that the slip length is independent of the shear rate and the density,
and proportional to the BGK relaxation time. The method is used to study slip
in Poiseuille flow and in linear shear flow. Patterned walls with stripes of
different slip parameters are also studied, and an anisotropy of the slip
length in accordance with the surface pattern is found. The angle dependence of
the simulation results perfectly agrees with theoretical expectations. The
results confirm that the proposed boundary conditions can be used for
simulating slip-flows in micro fluidics using single relaxation time lattice
Boltzmann, without any numerical slip, giving an accuracy of the second order.
