Optimization Schemes for Selective Molecular Cleavage with Tailored Ultrashort Laser Pulses

TL;DR

This paper develops computational methods to design ultrashort laser pulses for selective molecular bond breaking, using a mixed quantum-classical approach and various optimization algorithms.

Contribution

It introduces new optimization schemes for tailoring laser pulses to achieve specific molecular cleavages using a mixed quantum-classical model.

Findings

Effective pulse shaping based on force, momentum, and velocity criteria.

Comparison of gradient-free and optimal control algorithms.

Successful application to atomic chain models and real molecules.

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.