A typical nanotribology simulation setup is the semi-infinite substrate, featuring a sliding bead on top and with the lower substrate layers thermostatted to control temperature. A challenge is dealing with phonons that backreflect from the substrate lower boundary, as these will artificially reduce the friction $F_{\mathrm{fr}}$ acting on the sliding bead. One proposed solution is to use a Langevin thermostat, operating at temperature $T_{\mathrm{lan}}$, and with the corresponding damping parameter $\gamma$, optimally tuned such that $F_{\mathrm{fr}}$ is maximized [Benassi et al., Phys. Rev. B 82, 081401 (2010)]. In this paper, the method is revisited and related to the substrate phonon lifetime, the substrate temperature $T_{\mathrm{sub}}$, and the sliding speed. At low sliding speed, where the time between stick-slip events is large compared to the phonon lifetime, we do not observe much dependence of $F_{\mathrm{fr}}$ on $\gamma$, and here thermostat tuning is not required. At high sliding speed, upon varying $\gamma$, we confirm the aforementioned friction maximum but also observe a pronounced minimum in $T_{\mathrm{sub}}$, which here deviates from $T_{\mathrm{lan}}$. For substrate particle interactions that are strongly anharmonic, the variation of $F_{\mathrm{fr}}$ with $\gamma$ can be understood as a manifestation of thermolubricity, backreflections being essentially unimportant. In contrast, for harmonic interactions, where phonon lifetimes become very long, $F_{\mathrm{fr}}$ is strongly affected by backreflecting phonons, though not enough to overturn thermolubricity.

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• Friction
• Phonons
• Molecular dynamics