Abstract
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 acting on the sliding bead. One proposed solution is to use a Langevin thermostat, operating at temperature , and with the corresponding damping parameter , optimally tuned such that 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 , 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 on , and here thermostat tuning is not required. At high sliding speed, upon varying , we confirm the aforementioned friction maximum but also observe a pronounced minimum in , which here deviates from . For substrate particle interactions that are strongly anharmonic, the variation of with can be understood as a manifestation of thermolubricity, backreflections being essentially unimportant. In contrast, for harmonic interactions, where phonon lifetimes become very long, is strongly affected by backreflecting phonons, though not enough to overturn thermolubricity.
1 More- Received 8 April 2019
- Revised 8 August 2019
DOI:https://doi.org/10.1103/PhysRevB.100.094305
©2019 American Physical Society