Simulating excited-state processes in nanostructures using time-dependent density functional theory-based Ehrenfest dynamics

Ari Ojanperä

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Many phenomena and processes in nature are related to excited electronic states and their time development, for example light absorption, fluorescence and ion-atom collisions. Moreover, many experimental methods such as femtosecond pump-probe laser spectroscopy and photo-emission spectroscopy rely on processes related to excited electronic states. Consequently, a proper description of the excited electron-ion system and the coupled electron-ion dynamics is crucial for the understanding of excited-state processes, interpreting a large amount of experimental data collected with methods that involve electron excitation as well as for developing new technology based on excited-state phenomena. Especially the modeling of nonadiabatic coupled electron-ion motion, which incorporates interactions between the wavefunctions of the electrons and the nuclei, poses an extremely tough challenge. Not only are the wavefunctions themselves cumbersome to model, but simulating the nonadiabatic dynamics of electrons and nuclei to a reasonable accuracy is a highly difficult theoretical and computational task. During the recent years, a method called Ehrenfest dynamics has been successfully used for simulating nonadiabatic electron-ion dynamics in conjunction with the time-dependent density functional theory (TDDFT). It has been successfully applied to studying, for example, ion bombardment of carbon, gold and aluminium targets, photoexcitation dynamics of biomolecules and excited-state carried dynamics in carbon nanotubes. Typical Ehrenfest dynamics implementations are based on pseudopotentials, which simplify the implementation as compa-red to the projector augmented-wave (PAW) method or localized basis function sets. The PAW method generally increases the accuracy of the calculations as compared to pseudopotential-based calculations. The main result of this thesis is the development and implementation of Ehrenfest dynamics within the PAW formalism. The formalism has been implemented to the electronic structure program GPAW. The implemented Ehrenfest dynamics method is used for two applications motivated by experimental findings: ion bombardment of graphene sheets and dynamics of a ligand-protected gold cluster after excitation by light. In this thesis Ehrenfest dynamics equations are also derived for the combination of localized basis functions sets and the PAW method. Special focus is given to the rigorous derivation of the quantum-classical forces from the Lagrangian action integral.
Translated title of the contributionNanorakenteiden ei-adiabaattisten prosessien mallintaminen ajasta riippuvaan tiheysfunktionaaliteoriaan perustuvalla Ehrenfestin dynamiikalla
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Puska, Martti, Supervising Professor
  • Havu, Ville, Thesis Advisor
  • Lehtovaara, Lauri, Thesis Advisor, External person
Publisher
Print ISBNs978-952-60-6645-5
Electronic ISBNs978-952-60-6646-2
Publication statusPublished - 2016
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • TDDFT
  • Ehrenfest dynamics
  • PAW method
  • localized basis function sets

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