  We present some approaches to the computation of ultra-fast laser pulses
capable of selectively breaking molecular bonds. The calculations are based on
a mixed quantum-classical description: The electrons are treated quantum
mechanically (making use of time-dependent density-functional theory), whereas
the nuclei are treated classically. The temporal shape of the pulses is
tailored to maximise a control target functional which is designed to produce
the desired molecular cleavage. The precise definition of this functional is a
crucial ingredient: we explore expressions based on the forces, on the momenta
and on the velocities of the nuclei. The algorithm used to find the optimum
pulse is also relevant; we test both direct gradient-free algorithms, as well
as schemes based on formal optimal control theory. The tests are performed both
on one dimensional models of atomic chains, and on first-principles
descriptions of molecules.
