Optimization Schemes for Selective Molecular Cleavage with Tailored Ultrashort Laser Pulses

Abstract

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.

51 pages

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• Optimal control theory for quantum-classical systems: Ehrenfest Molecular Dynamics based on time-dependent density-functional theory
• Searching for an optimal control in the presence of saddles on the quantum mechanical observable landscape
• Optimal control of interacting quantum systems based on the first-order Magnus approximation: Application to multiple dipole-dipole coupled molecular rotors
• Optimal control with non-adiabatic Molecular Dynamics: application to the Coulomb explosion of Sodium clusters
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