QUANTUM DYNAMICS OF EXCITED ELECTRONS FROM FIRST PRINCIPLES: HOT CARRIER RELAXATION AND ELECTRONIC STOPPING Public Deposited

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  • March 21, 2019
Creator
  • Reeves, Kyle
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • An understanding of dynamical properties of matter is often essential to developing a deeper understanding of systems and their behavior. Many important examples of complex electron dynamics are a result of excited systems such as in the photoexcitation of photosynthetic complexes or hot carrier relaxation in photovoltaic devices. Applying first-principles computational methods to describe these systems and their dynamics would be a valuable tool to gain a deeper understanding of the relationship between atomic structure and the non-equilibrium electron dynamics. Approaches based on the Born-Oppenheimer adiabatic approximation fail, however, as the separation of electron and nuclear motion is no longer valid in the presence of excited electrons. First-principles simulations that incorporate non-adiabatic effects represent an approach to properly simulating the quantum dynamics of excited electrons while maintaining predictive power. In this work, we investigate two non-adiabatic phenomena while at the same time maintaining atomistic-level detail. These two phenomena are hot-carrier relaxation in silicon quantum dots and electronic stopping power in liquid water. We conclude that in nanoscale systems, excited electron relaxation dynamics are sensitive to the surface passivation. Using a fewest-switches surface hopping approach, we identified a unique electronic state that appears in nanocrystalline sillicon when passivated by fluorine that acts as a “shuttle state” to extend the iv electron relaxation rate, by a factor of five compared to an identical system passivated by hydrogen. To simulate electronic stopping in water, we use real-time time-dependent density functional theory simulations to capture the energy transfer process from high-energy protons and alpha-particles (1MeV-10MeV) into liquid water. We report the first ab initio electronic stopping power curve for liquid water. Additionally, we use the real-time electron density to offer a qualitative interpretation of the electron dynamics. We observe a greater contribution of lone pair electrons compared to electrons in the OH bond during the excitations of individual molecules involved in the electronic stopping process. Finally, we conclude that the effective charge of energetic ions in liquid phases result in a significant suppression of excitations by an order of magnitude compared to the excitations observed in the gas phase.
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Rights statement
  • In Copyright
Advisor
  • Berkowitz, Max
  • Moran, Andrew
  • Atkin, Joanna
  • Kanai, Yosuke
  • Cahoon, James
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016
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