First-principles theory of atomic-scale friction

We determine the atomic-scale friction associated with a layer of Pd atoms moving across a graphite substrate from ab initio total-energy calculations. We evaluate the friction energy caused by variations of the chemical bond strength and work against an external force (load) due to variations of the bond length along the trajectory. We find only a very small dependence of the Pd-graphite interaction on the adsorption site which gives rise to a very small friction coefficient \ensuremath{\mu}\ensuremath{\approxeq}${10}^{\mathrm{\ensuremath{-}}2}$ for loads near ${10}^{\mathrm{\ensuremath{-}}8}$ N. We also find \ensuremath{\mu} to increase with load in agreement with recent experiments.