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A typical nanotribology simulation setup is the semi-infinite substrate,featuring a sliding bead on top, and with the lower substrate layersthermostatted to control temperature. A challenge is dealing with phonons thatbackreflect from the substrate lower boundary, as these will artificiallyreduce the friction FR acting on the sliding bead. One proposed solution is touse a Langevin thermostat, operating at temperature TLAN, and with thecorresponding damping parameter, GAMMA, optimally tuned such that FR ismaximized [Benassi etal, PHYSREVB, V82, P081401, 2010]. In this paper, themethod is revisited, and related to the substrate phonon lifetime, thesubstrate temperature TSUB, and the sliding speed. At low sliding speed, wherethe time between stick-slip events is large compared to the phonon lifetime, wedo not observe much dependence of FR on GAMMA, and here thermostat tuning isnot required. At high sliding speed, upon varying GAMMA, we confirm theaforementioned friction maximum, but also observe a pronounced minimum in TSUB,which here deviates from TLAN. For substrate particle interactions that arestrongly anharmonic, the variation of FR with GAMMA can be understood as amanifestation of thermolubricity, backreflections being essentiallyunimportant. In contrast, for harmonic interactions, where phonon lifetimesbecome very long, FR is strongly affected by backreflecting phonons, though notenough to overturn thermolubricity.

On the connection between sliding friction and phonon lifetimes: Thermostat induced thermolubricity effects in molecular dynamics simulations