Abstract

Investigating the dynamics of photoexcited molecules usually involves overcoming the obstacles that arise due to the breakdown of the Born-Oppenheimer approximation. Over the last decades, a substantial number of methods have been developed to reach this goal, employing differnt ways to approximate the solution of the time-dependent molecular Schr¨odinger equation. In this talk, I will give an overview of different aspects of
nonadiabatic dynamics, starting from state of the art applications for interpreting experimental results before moving to theoretical considerations and details of development of new molecular dynamics methods. I will introduce and highlight the different strengths and limitations that theoretical and computational methods face towards the goal of enabling a complete in-silico photochemical experiment.

First, I will highlight how computational tools are indispensable for the investigation of photochemical reactions of complex molecules. In the context of a recent joint experimental-theoretical study, I will show how theory allows us to explain the mechanistic details of the initial ultrafast ring-opening of thiophenone, its subsequent ground state dynamics and the resulting formation of several vibrationally excited photoproducts [1].

I, then, will introduce the challenges faced by nonadiabatic dynamics which open future directions of my research and I will describe my attemps and ideas to tackle them. I will give insights and open questions about the theoretical picture that is commonly used to describe photochemical processes. To introduce the challenges and necessity of describing light-matter interaction explicitly with the most popular formalisms, the
photoisomerization of a three-dimensional Retinal chromophore model [2] will be investigated with coupled trajectory methods [3, 4] accounting for the effects of different couplings as well as varied photoexcitation processes. Subsequently, I will bridge from theoretical and methodological developments towards simulations of real, full-dimensional molecules.[5]

Overall, I want to present a complete picture of theoretical photochemistry, from where we stand at the moment until how the current methodologies can be advanced to overcome limitations to their application.

(1) Pathak, S. et al. Nat. Chem. 2020, 12, 795–800.
(2) Marsili, E.; Olivucci, M.; Lauvergnat, D.; Agostini, F. J. Chem. Theory Comput. 2020, 16, 6032–6048.
(3) Min, S. K.; Agostini, F.; Tavernelli, I.; Gross, E. K. U. J. Phys. Chem. Lett. 2017, 8, 3048–3055.
(4) Pieroni, C.; Agostini, F. J. Chem. Theory Comput. 2021, 17, 5969–5991.
(5) Ibele, L. M.; Curchod, B. F. E. Phys. Chem. Chem. Phys. 2020, 22, 15183–15196.