Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

The motion of electrons plays a fundamental role in both physics and chemistry, and capturing such dynamics requires the ability to resolve changes at the attosecond timescale, which is enabled by the advent of ultrashort laser pulses. This dissertation aims to facilitate the interpretation of ultrafast electron dynamics and attosecond spectroscopy by real-time time-dependent density functional theory (RT-TDDFT) simulations. The first part of this dissertation focuses on improving the simulation of X-ray transient absorption spectra (XTAS) with Gaussian basis sets in RT-TDDFT by applying a filter to the transition dipole matrix. Due to the spatial limitation of atom-centered Gaussian functions, the transitions from higher-energy orbitals to the poorly described continuum can show as “intruder” peaks in the simulated core-level spectra. This can further result in un- physical modulations in the calculated XTAS, leading to incorrect interpretations of the corresponding electron dynamics. By manually zeroing all elements arising from unwanted transitions, the calculated XTAS are free of these unphysical peaks. This methodology can be adapted to other Gaussian-based real-time methods. In the second part of this dissertation, a combination of RT-TDDFT and scattering theory is employed to calculate time-resolved X-ray scattering and explore the potential mapping between the scattering signals and electron dynamics. The investigations of the electron motions induced by core-hole ionization or a UV pump in both ring-shape and linear molecules reveal measurable modulations between the electron currents and the scattering patterns.

Date

6-15-2023

Committee Chair

Lopata, Kenneth

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