Ab initio methods for atmospheric photochemistry

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

The interaction of molecules with sunlight has always played a crucial role in determining the chemical composition of the atmosphere. In this thesis, I intend to explore how describing photochemical reactions in silico can bridge the gap between performing a single-point
electronic structure calculation, and being able to predict the rates of photochemical reactions.
Photolysis rates in models of atmospheric chemistry are frequently calculated from the measured absorption cross section. There are a number of methods for reproducing the broadening of excitation bands when this spectrum is unavailable, which I will test on a selection of atmospheric molecules so as to design a set of guidelines for selecting an appropriate strategy in each case.
One of these molecules, a hydroperoxy aldehyde, is of particular interest due to the role that nonadiabatic effects play in its photolysis. Using this model system I test an extension of the energy-grained master equation which factors in nonadiabatic transitions between different electronic states by comparing it to fully atomistic nonadiabatic dynamics. Looking at nonadiabatic processes in the excited state through a kinetic lens allows us to model the rate of population transfer between diabatic states when it is in the ergodic regime, with highly accurate transition probabilities obtained through Zhu-Nakamura theory.
In later chapters, I also explore and implement a novel nonadiabatic dynamics protocol, and apply explicit and implicit solvation methods in two case studies of photochemical reactivity.
Date of Award28 Sep 2021
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorDavid Glowacki (Supervisor) & Andrew J Orr-Ewing (Supervisor)

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