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M. Wolloch, G. Feldbauer, P. Mohn, J. Redinger, A. Vernes:
"Ab initio friction forces on the nanoscale: A density functional theory study of fcc Cu(111";
Physical Review B, 90 (2014), 1954181 - 1954188.

While there are a number of models that tackle the problem of calculating friction forces on the atomic level,
providing a completely parameter-free approach remains a challenge. Here we present a quasistatic model to
obtain an approximation to the nanofrictional response of dry, wearless systems based on quantum-mechanical
all-electron calculations.We propose amechanism to allowdissipative sliding, which relies on atomic relaxations.
We define two different ways of calculating the mean nanofriction force, both leading to an exponential frictionversus-load behavior for all sliding directions. Since our approach does not impose any limits on the lengths and directions of the sliding paths, we investigate arbitrary sliding directions for an fcc Cu(111) interface and detect two periodic paths that form the upper and lower bound of nanofriction. For long aperiodic paths, the friction force converges to a value in between these limits. For low loads, we retrieve the Derjaguin generalization of the Amontons-Coulomb kinetic friction law, which appears to be valid all the way down to the nanoscale. We observe a nonvanishing Derjaguin offset even for atomically flat surfaces in dry contact.