Résumé
The accurate description of quantum effects, particularly quantum tunneling[1], in bimolecular chemical reactions constitutes one of the major goals of theoretical chemistry. Due to an unfavorable scaling law, exact quantum scattering methods lead to expensive and often unfeasible simulations when considering chemical systems with a large number of degrees of freedom. Moreover, at low temperature quantum effects often do not represent a small correction to classical calculations, but contrariwise are essential to obtain quantitative results.In this talk, I will show the feasibility of accurate quantum stationary scattering simulations for high dimensional systems using hybrid quantum-classical trajectories[2]. The configuration space is partitioned in one reaction coordinate going from reactants to products along which trajectories reproduce quantum effects, and bath coordinates with small amplitude motion which are treated classically[3]. Quantization of bath modes by a semi-classical phase-space sampling approximation based on Wigner-Weyl mapping allows to accurately reproduce quantum structure effects such as reaction thresholds. As was acknowledged many years ago [4], when the motion along the reaction coordinate is sufficiently slow compared to perpendicular motion, both subsystems undergo adiabatic evolution. By taking advantage from the local character of trajectory dynamics, I will illustrate how on-the-fly conversion from position-momenta to action-angle representation for bath coordinates in specific regions of vibrational adiabaticity leads to a computationally efficient scheme[5].