Short-time molecular simulations of ionizing irradiation of plutonium extractant solutions

This thesis deals with ultra-short-time (attosecond-femtosecond) simulations of irradiation of molecules by massive ionizing particles. In many fields such as nuclear or medical, the products and mechanisms of degradation are followed by the scientific community. The simulations were carried out using the deMon2k code and divided into three chapters. The first chapter deals with the electronic response of the tributyl phosphate (TBP) molecule and inorganic complexes formed with plutonium in the gas phase, irradiated to high-energy alpha particles. Electronic response and generation of secondary electron are simulated by real-time propagation of time-dependent auxiliary density functional theory (RT-TD-ADFT) equations. In addition, we describe the implementation within deMon2k of static and adaptive absorbing boundary conditions. We show that the choice of absorbing conditions in the space of molecular orbitals enables electrons to be absorbed during dynamics, after irradiation. We show that the different responses of the electron cloud differ depending on whether we consider the free or complex form of TBP. The second chapter focuses on the problem of sampling the electronic dynamics performed by RT-TD-ADFT to obtain the electronic stopping power, a property that is highly dependent on impact parameters. The promising solution we propose, tested for bulk water, is the use of neural networks, trained from electrostatic interactions between a charged ionizing particle and the atoms in the system, to predict electronic stopping power. Finally, a third chapter focuses on the dissociative electronic attachment of TBP generated by secondary electrons after irradiation. While the anionic form of the system simulates electronic attachment, we have implemented in deMon2k a computational method based on ab initio molecular dynamics and on the addition of excess atomic kinetic energy, to simulate chemical bond breaking in the gas and condensed phases. The manuscript concludes with a general summary of the work and a proposal for possible future research avenues. (author)