  A single graphene layer placed between two parallel Ni(111) surfaces screens
the strong attractive force and results in a significant reduction of adhesion
and sliding friction. When two graphene layers are inserted, each graphene is
attached to one of the metal surfaces with a significant binding and reduces
the adhesion further. In the sliding motion of these surfaces the transition
from stick-slip to continuous sliding is attained, whereby non-equilibrium
phonon generation through sudden processes is suppressed. The adhesion and
corrugation strength continues to decrease upon insertion of the third graphene
layer and eventually saturates at a constant value with increasing number of
graphene layers. In the absence of Ni surfaces, the corrugation strength of
multilayered graphene is relatively higher and practically independent of the
number of layers. Present first-principles calculations reveal the
superlubricant feature of graphene layers placed between pseudomorphic Ni(111)
surfaces, which is achieved through the coupling of Ni-3d and graphene-$\pi$
orbitals. The effect of graphene layers inserted between a pair of parallel
Cu(111) and Al(111) surfaces are also discussed. The treatment of sliding
friction under the constant loading force, by taking into account the
deformations corresponding to any relative positions of sliding slabs, is the
unique feature of our study.
