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 maximize 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.
Bibliographical noteFunding Information:
This work was partially supported by the Deutsche Forschungsgemeinschaft within the SFB 658, and by the research project FIS2009-13364-C02-01 (MICINN, Spain).
- Quantum optimal control theory
- Time-dependent density-functional theory