Theory of Friction with Applied Load

We present a molecular dynamics simulation for the static friction under the effect of load. We chose a system formed by slabs of molecules of N ₂ deposited on a (111) surface of Pb. In contrary to many calculations, we assume that the Pb atoms are not kept fixed in the lattice positions, but can vibrate in their own phonon’s field. This has the important consequence that the upper and lower block can exchange energy and momentum. During the molecular dynamics simulation, the two systems can reach a thermodynamical equilibrium. When in our molecular dynamics simulation the equilibrium is reached the N ₂ plane at the interface reconstructs. The unit cell is still hexagonal but it contains 16 molecules in disordered positions. These positions of the N ₂ molecules are strongly modified by the presence of load. For small load there is a small increase of the disorder that produces a small reduction in the static friction. For larger loads the formation of clusters begins, and for high loads the size of the clusters increases and there is a tendency to the formation of vacancies. These effects are producing a large increase in the force friction. We can then distinguish different regions that characterize the behaviour of the static friction as a function of the load.