of magnitude in length scale.

Methods {#sec:Meth}
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As a prototype system to study our nanofriction model we consider two atomically flat slabs of fcc(111) copper in dry contact, represented by a $1\times 1$ hexagonal unit cell (see Fig. \[fig:0\]). Both slabs are described by two rigid Cu layers (grey spheres) representing the transition to Cu-bulk followed by a tribologically active zone consisting of four Cu layers (red spheres) which are allowed to relax in 3 dimensions. In preliminary calculations the addition of an additional free layer was found to not significantly change the resulting geometries even at the positions with the highest stresses. External loads are imposed by keeping the rigid layers at a given distance smaller than the equilibrium one. The full simulation box consists of 12 atoms using a bulk lattice constant $a=\unit[3.634]{\AA}$ determined from DFT equilibration, cf. in experiments $a=\unit[ 3.615]{\AA}$ [@wyckoff:63]. Due to the inherent periodicity of our supercell, a vacuum layer of about is included on top of the upper slab to decouple the periodically repeated simulation cell in the z direction. This 12 layer thick arrangement is comparable to a number of previous studies using *ab-initio* methods [@dag:04; @neitola:06; @wieferink:11; @zhang:11; @garvey:11a; @garvey:11b; 