  Using a tight-binding atomistic simulation, we simulate the recent
atomic-force microscopy experiments probing the slipperiness of graphene flakes
made slide against a graphite surface. Compared to previous theoretical models,
where the flake was assumed to be geometrically perfect and rigid, while the
substrate is represented by a static periodic potential, our fully-atomistic
model includes quantum mechanics with the chemistry of bond breaking and bond
formation, and the flexibility of the flake. These realistic features, include
in particular the crucial role of the flake rotation in determining the static
friction, in qualitative agreement with experimental observations.
