$[\,1\,1\,\overline{1}\,]$ direction. The y-direction points into the $[\,\overline{1}\,1\,0\,]$ direction and is in the plane spanned by $a_1$ and $a_2$ and orthogonal to the x-axis.[]{data-label="fig:1"}](Fig1.pdf){width="1.0\linewidth"}

A central feature in the description of friction is to allow dissipative sliding. In principle, any modeling that involves smooth continuous energy surfaces, such as we get from our grid approach when using only the fully relaxed system, means that one moves on a conservative energy landscape, resulting in energy neutral displacements and frictionless sliding. An earlier *ab-initio* attempt to tackle this problem has been developed by Zhong and Tománek et al. [@zhong:90; @tomanek:91] who studied the stick-slip motion of single atom tips over graphite. In contrast to their approach and in order to describe the portion of energy lost into heat, we propose the following mechanism. Along each path we identify the local minima and maxima on the energy curve of the unrelaxed system. We assume static sliding without relaxations until a maximum in the energy is encountered, which in our model is representative of the “stick” phase of stick-slip sliding. At this point we allow the built up strain to be released by relaxing the tribologically active zone (the first part of the “slip” 