fcc Cu(111) slabs sliding along a $10^\circ$ path. The insert (black crosses) shows the difference $F^{(2)}-F^{(1)}$. At low to medium loads the difference is constant and corresponds to the disparity of the friction at zero load $F_0$[]{data-label="fig:6"}](Fig6.pdf){width="1.0\linewidth"}

The largest load considered in our simulations is $\unit[367]{pN}$, given the cross-section area of the unit cell $\unit[5.7]{\AA^2}$, this is equivalent to a static pressure of $\unit[6.4]{GPa}$ which is well beyond any realistic technological applications. Thus, it is important to analyze the low load regime of up to () separately. In this range the exponential law can be approximated reasonably well by a linear relation $F_{\mathrm{lin}}(L)=F_0+\mu_{\mathrm{lin}} L$ so that the COF $\mu_{\mathrm{lin}}$ is given by the slope, see Tab. \[tab:coefficients\]. It should be noted that the $\mu_{\mathrm{lin}}$ obtained in this manner are systematically larger than the values of $\mu$, since the slope of a linear fit to a segment of an exponential function is always steeper than the tangent of the function at the beginning of the segment. Since the ultimate tensile strength for annealed copper is approximately $\unit[160]{MPa}$ [@yu:04] an uniaxial pressure of more than will already deform the sample. However, it remains computationally feasible to study extremely high loads because the 