Despite enormous progress in algorithms and computing power, routine atomistic molecular dynamics (MD) simulations remain limited to the microsecond timescale. The reason is that the allowed time step for the time integration of the trajectories is set by the fastest molecular motions. For large time steps, time integration becomes unstable, primarily because deep particle collisions or fast bond vibrations result in large forces that at the next time step amplify the stability problem. The default time step of ∼2 fs in classical MD of biomolecules is below the stability limit, so that deep collisions and the resulting catastrophic crashes are virtually impossible to occur in any simulation of reasonable length for any accessible system size.