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Photochemistry: dynamic aspects

At the interface between quantum and classical mechanics, so-called quantum-classical simulation methods are introduced based on the theory of exact factorization of the molecular wave function [Agostini2021]. This theory is at the forefront of international efforts in the physical chemistry community to go beyond the Born-Oppenheimer approximation. In this approach, the coupled dynamics of electrons and nuclei in a molecule are approximately described using trajectories with a pseudo-classical description for the nuclei and wave function based quantum description for the electrons.

The goal of these theoretical and computational developments is to propose molecular dynamics algorithms for excited electronic states, suited to describing various photochemical reactions, such as trans-cis photoisomerization in azobenzene [Pieroni2024] or the dynamics of uracil after ionization [Villaseco-Arribas2023]. These reactions are characterized by ultrafast non-radiative de-excitation phenomena through conical intersections [Ibele2022] and intersystem crossings [Talotta2020].

Our interest in photochemistry applications is accompanied by theoretical developments on the fundamental aspects of exact factorization theory. For example, we study geometric phase effects, such as the Berry phase, in dynamics near conical intersections [Ibele2023], within the framework of an international collaboration with Durham University (UK). In collaboration with the University of Montpellier, we have combined exact factorization with the concept of quantum trajectories to describe phenomena like tunneling. Recently, purely electronic exact factorization has been used for developments in density functional theory.

Dynamics study in the vicinity of a conical intersection using exact factorization compared to a standard approach

Collaborations

Nathalie Rougeau and Sabine Morisset (ISMO, U. Paris-Saclay), Yohann Scribano (LUPM, U. Montpellier), Marco Schirò (JEIP, Collège de France), Massimo Olivucci (University of Siena, Italy), Maurizio Persico and Giovanni Granucci (U. Pisa, Italy), Basile F. E. Curchod (U. Bristol, England), Neepa T. Maitra (Rutgers University, USA).

When light-matter interactions specifically involve certain degrees of freedom, the environment is described in the open quantum systems method through statistical tools calibrated by ab initio data. We primarily deal with non-adiabatic electronic dynamics under a field coupled with the thermal reservoir of nuclear vibrations [Chin2019, Mangaud2019, Le Dé2024]. Our propagation methods, based on the recent tensor train technique [Mangaud2023], allow us to simulate stationary or time-dependent spectra and analyze the optical control of a system subject to decoherence, such as the creation of electronic state superpositions in PPE-type polymers [Breuil2021, Jaouadi2022], using various algorithms including reinforcement learning [Jaouadi2024].

In addition to systems influenced by their environment, quantum dynamics simulations in small isolated systems remain crucial for elucidating experimental results such as the photodissociation of N2+ [Ayari2020] or the control of RbSr photoassociation to prepare ultracold molecules [Devolder2021].

Application where a laser field prepares coherence between two electronic states to create an asymmetry in a symmetric dimer. The environment consists of nuclear vibrators that cause fluctuations in energies and electronic coupling. The dynamics are treated by HEOM (Hierarchical Equations of Motion), and the optimal field is determined by coupling HEOM with a reinforcement learning algorithm.

Collaborations

Etienne Mangaud, Majdi Hochlaf (MSME, U. Gustave Eiffel), Benjamin Lasorne (ICGM, U. Montpellier), Alex Chin (INSP, Sorbonne U.), Amine Jaouadi (LYRIDS, ECE-Paris), Laurent Nahon (Synchrotron-Soleil), Olivier Dulieu (Laboratoire A. Cotton, U. Paris-Saclay).