New Numerical Approaches for Short-Time Radiolysis
The currently emerging field of Attosecond spectroscopy offers the potential to study ultrashort times (<ps) in radiolysis, which were previously inaccessible with pulsed radiolysis methods. This in turn has stimulated the development of new ab initio simulation approaches [Loh2020, Jordan2020, Omar2021]. Chemistry under ionizing radiation differs significantly from photochemistry due to the magnitude of the energy involved during irradiation and the resulting multi-scale responses. We have developed a set of methods based on the ADFT formalism to simulate energy deposition mechanisms, ionization, non-adiabatic nuclear response, and radio-induced chemical reactivity in complex and inhomogeneous molecular systems such as proteins [Omar2023].

RT-TD-ADFT/MM simulations of the irradiation of a DNA oligomer by fast ions have enhanced our understanding of the ionization mechanism and the sites of secondary electron emission.
Energy Deposition by Fast Ions and XUV Photons
Building on the effectiveness of the RT-TD-ADFT module of the deMon2k code, we have tackled the mechanisms of energy deposition and ionization in complex molecular systems. In the framework of Damien Tolu's thesis [Tolu-Thèse2023], we are collaborating with Dominique Guillaumont from CEA Marcoule to study the degradation of Pu(IV) complexes relevant to the nuclear industry [Tolu2023]. In biological systems, we have published the first simulations of irradiation by H+, He2+, or C6+ ions on a solvated DNA oligomer (Figure), providing valuable insights into the physical stage of irradiation [Alvarez-Ibarra2020]. Additionally, in Karvan Omar's thesis [Omar-Thèse2023], we investigated the ionization of small proteins by XUV photons to aid in the interpretation of innovative attosecond pump-probe experiments.
The quantification of energy deposition is evaluated by the electronic stopping power. In collaboration with Eleonora Luppi (LCT, Sorbonne U.), we demonstrated that accurate description of continuum states is a crucial parameter for the precision of these calculations. One solution, using a program with localized atomic orbitals, is to enhance the standard Gaussian basis sets with functions tailored to describe the continuum states. A recent paper providing an extensive benchmark on basis set effects has been published, offering a reference starting point for our future studies [Tandiana2023].
Collaborations
Dominique Guillaumont (CEA Marcoule), Franck Lépine (ILM, U. Lyon), Eleonora Luppi (LCT, Sorbonne U.).