TYC soiree: Non-adiabatic dynamics

Theory and simulation of ultrafast processes in molecules – Federica Agostini, Sorbonne University, Paris

The interaction of light and matter is responsible for a variety of photophysical and photochemical phenomena occurring in nature, like photosynthesis, in the human body, like vision, and in technological devices, like photovoltaics. Theoretical modeling of these phenomena requires to be able to describe the complex interplay of electronic and nuclear motion beyond the Born-Oppenheimer approximation [1], ie including nonadiabatic effects, over ultrafast time scales ranging from femtoseconds to picoseconds.

The exact factorization of the electron-nuclear wavefunction is a formalism introduced in 2010 by Gross and coworkers to analyze and to simulate nonadiabatic processes [2]. Its original electron-nuclear formulation has been used to derive various flavors of trajectory-based algorithms [3,4] to simulate ultrafast relaxation processes initiated by photoexcitation, like photoisomerizations or photodissociations. However, extensions of the original formalism to treat electron-only systems (exact electron factorization) and photon-electron-nuclear systems (exact photon-electron-nuclear factorization) have been proposed to develop density functional theory or to study photodynamics in the strong light-matter coupling regime [5]. 

In this talk, I will present an introduction to the theory of nonadiabatic ultrafast dynamics with the exact factorization and I will give an overview of its recent applications.

[1] F. Agostini, B. F. E. Curchod, WIREs Comput. Mol. Sci. (2019).
[2] L.-M. Ibele, E. Sangiogo Gil, E. Villaseco Arribas, F. Agostini, Phys. Chem. Chem. Phys. (2024).
[3] C. Pieroni, E. Sangiogo Gil, L.-M. Ibele, M. Persico, G. Granucci, F. Agostini,  J. Chem. Theory Comput. (2024).
[4] L.-M. Ibele, E. Sangiogo Gil, P. Schürger, B. Le Dé, R. Noc, F. Agostini,  J. Chem. Theory Comput. (2026).
[5] S. Giarrusso, P. Schürger, F. Agostini, arXiv:2602.23914 [physics.chem-ph] (2026).

Improving the accuracy of nonadiabatic surface-hopping simulations – Jonthathan Mannouch, MPSD, Hamburg, Germany

Fewest-switches surface hopping (FSSH) is one of the most popular approaches for simulating photochemical experiments [1], even though it suffers from problems of inconsistency and overcoherence that often significantly degrade its accuracy.

For example, FSSH is unable to correctly describe the dynamics under strong electromagnetic pulses [2,3], such that a fully satisfactory approach for simulating the photoexcitation step of many experiments is currently lacking. Additionally, using FSSH in systems containing a dense manifold of electronic states is also challenging
[4,5], because trivial crossings must be correctly accounted for.

In this talk, I will discuss some of my recent work in alleviating these problems in surface-hopping based simulations. First, I will demonstrate how the advantageous features of a newly developed surface-hopping algorithm (the mapping approach to surface hopping [6]) can be utilized to provide an improved description of the photoexcitation step for a series of molecular systems. Finally, I will present an improved expression for the FSSH hopping probability, which in tandem with state tracking provides a robust strategy for computing charge mobilities in molecular materials.

[1] J. E. Subotnik et. al., Annu. Rev. Phys. Chem. 2016, 67, 387–417.
[2] B. Mignolet, B. F. E. Curchod, J. Phys. Chem. A 2019, 123, 3582–3591.
[3] T. Fiedlschuster, et al., Phys. Rev. A, 95, 063424 (2017)
[4] T. Qiu, C. Climent, J. E. Subotnik, J. Chem. Theory Comput. 19, 2744-2757 (2023)
[5] A. Carof, S. Giannini, J. Blumberger, Phys. Chem. Chem. Phys. 21, 26368 (2019)
[6] J. R. Mannouch, J. O. Richardson, J. Chem. Phys. 2023, 158, 104111.