Electron Dynamics From First-Principles Quantum Theory: Electronic Stopping and Wannier Function Propagation

Developing a predictive understanding of the behaviors of molecules and materials requires examination of the underlying electron dynamics. The response of quantum mechanical particles like electrons to perturbations such as ion and photon radiation needs to be described through the framework of quantum theory. In particular, first-principles approaches are well-suited for simulating electron dynamics in matter. Without any reliance on empirical fitting, first-principles simulations can provide quantitatively accurate predictions for properties related to electron dynamics, and they can give details of how these properties derive from the complex interplay between electrons and nuclei. The scientific insights gained from such simulation studies can aid in the advancement of radiation oncology, nuclear cladding, photovoltaic cells, and other technologies. This dissertation comprises studies of electron dynamics in a range of systems through a simulation framework based on real-time, time-dependent density functional theory (RT-TDDFT). The majority of the thesis focuses on the problem of electronic stopping. Electronic stopping is the energy transfer process from swift ions, such as protons and alpha-particles, to electrons in matter. The molecular-level details of this process are of great scientific interest, as is the accurate calculation of electronic stopping power, the rate of energy transfer from projectile ion to target electrons. Our non-equilibrium RT-TDDFT approach to simulating electronic stopping is greatly advanced throughout this dissertation work. Careful consideration of physical and numerical approximations has led to simulations of electronic stopping at the level of predictive accuracy. Taking advantage of these capabilities, the electronic stopping of DNA and water for protons and alpha-particles is studied, motivated by its importance in the field of ion beam radiation oncology. A molecular-level understanding of the electronic excitation response to ion irradiation in DNA and water is developed. The final portion of this thesis work details efforts to exploit the gauge freedom in RT-TDDFT through the propagation of maximally localized Wannier functions. Transforming time-dependent electronic orbitals into Wannier functions expands RT-TDDFT capabilities further to study various phenomena ranging from optical excitation, to electronic stopping, to topological charge transport. This methodological development paves the way for new and exciting applications of RT-TDDFT for studying electron dynamics.Doctor of Philosoph