@garvey:11c; @cahangirov:12; @j_wang:12; @cahangirov:13], and is sufficiently thick to approximate the elastic properties of copper while retaining computational efficiency.

![Sketch of the simulation cell containing 12 Cu atoms, tripled in the x and y direction for clarity. The top slab is displaced vertically to simulate several load conditions and in the x and y direction to collect data on energies and forces. Red atoms are allowed to relax, while grey atoms are kept rigid at their bulk-like positions. The gap at the interface is included for visual clarity and is of course not present under load when the slabs are compressed beyond their equilibrium distance.[]{data-label="fig:0"}](Fig0.pdf){width="0.51\linewidth"}

To investigate nanofrictional forces for sliding paths of different lengths and directions we apply a quasi-static grid approach, which means that the unit cell is sampled by choosing points on a regular grid for which the energies and forces are calculated (see Fig. \[fig:1\]). In addition to the advantage of being a parameter-free method, this concept ensures that the sliding direction can be chosen arbitrarily without recalculating energies and forces. The same holds for the length of the sliding path which can easily be extended to $\sim\unit[1]{\mu m}$, four orders of magnitude larger than the 