Connection between sliding friction and phonon lifetimes: Thermostat-induced thermolubricity effects in molecular dynamics simulations

Richard L. C. Vink
Phys. Rev. B 100, 094305 – Published 16 September 2019

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 Ffr acting on the sliding bead. One proposed solution is to use a Langevin thermostat, operating at temperature Tlan, and with the corresponding damping parameter γ, optimally tuned such that Ffr 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 Tsub, 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 Ffr on γ, and here thermostat tuning is not required. At high sliding speed, upon varying γ, we confirm the aforementioned friction maximum but also observe a pronounced minimum in Tsub, which here deviates from Tlan. For substrate particle interactions that are strongly anharmonic, the variation of Ffr with γ can be understood as a manifestation of thermolubricity, backreflections being essentially unimportant. In contrast, for harmonic interactions, where phonon lifetimes become very long, Ffr is strongly affected by backreflecting phonons, though not enough to overturn thermolubricity.

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  • Received 8 April 2019
  • Revised 8 August 2019

DOI:https://doi.org/10.1103/PhysRevB.100.094305

©2019 American Physical Society

Physics Subject Headings (PhySH)

  1. Research Areas
Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Richard L. C. Vink

  • Institute of Materials Physics, University of Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen, Germany

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Issue

Vol. 100, Iss. 9 — 1 September 2019

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