Simulations of contact formation beyond harmonic approximation:

Contribution from M. Müser (Germany)

The picture represents a tip (green atoms) that is modeled in a way such that long-range elasticity is included; not simply by harmonic springs but with anharmonic springs such that the proper pressure distribution in thecontact area is obtained ;-) There is some lubricant confined between tip and surface (red atoms), which is responsible for most of the shear forces. Of course, tip and substrate are incommensurate.