$50^\circ$ sliding path. The solid (cyan) line gives the energy for the unrelaxed slabs with the open (black) circles denoting local minima and maxima. The dashed (magenta) line shows the energy for the relaxed slabs with open (black) triangles marking the positions of the extrema of the unrelaxed slabs. The dotted (black) line is a schematic route for the calculation of the energy differences between the open circles and triangles, see equation (\[eq:F2\]).[]{data-label="fig:2"}](Fig2.pdf){width="1.0\linewidth"}

The use of unrelaxed energy curves, where the two bodies slide over each other statically, only adjusting their vertical distance to keep the load constant, is of course a rather crude assumption. However, for the two periodic sliding directions at $0^\circ$ and $30^\circ$ we also carried out more realistic shearing calculations that support our approach. In these calculations we use the same unit cell and drag the uppermost two (fixed) layers in small ($\sim\unit[0.1]{\AA}$) steps along the chosen sliding direction while holding the two bottom-most layers still. At each step the 8 free layers in the middle are allowed to relax and, in contrast to the quasi-static approach, these relaxed positions are the starting configuration for the next step. This method is only computationally practical for short 