Constructing a Hierarchy of Spawning-Based Methods for Nonadiabatic Molecular Dynamics

Abstract

The aim of this Thesis is to construct a multiple spawning (MS)-based hierarchy of
nonadiabatic molecular dynamics methods to study the photochemistry of molecular
systems. After an overview of the theoretical framework that sets the foundation for
the work presented in this Thesis, we move down the proposed hierarchy in the following
way: Starting at the top level, that is, ab initio multiple spawning (AIMS), we analyze the
sensitivity of this method with respect to its parameters. This sensitivity analysis is followed
by a stress-test of the recently introduced stochastic selection ab initio multiple spawning
(SSAIMS) method on the photodynamics of a set of three molecular systems – cyclopropanone,
fulvene, 1,2-dithiane – to fix its position in the MS hierarchy. However, since SSAIMS comes
with a new free parameter that has to be optimized by the user, we introduce in this Thesis a
new method that replaces this parameter with adaptable ones. This new method is applied to
three different molecules – ethylene, fulvene, cyclopropanone – to provide a proof of principle.
This method is then tested further on another set of molecular systems/models – a selection of
three two-dimensional two-state model systems, 1,2-dithiane and the organometallic complex
[Cr(CO)₆] – to establish its level in the MS hierarchy below SSAIMS and above the mixed
quantum-classical (MQC) method trajectory surface hopping (TSH). Finally, we study the
photochemistry of sulfine excited into its second excited state S2 . Based on TSH nonadiabatic
molecular dynamics trajectories we simulated the valence time-resolved photoelectron
spectrum (TRPES), a bona fide experimental observable.

Date of Award	4 Feb 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Basile F E Curchod (Supervisor) & Tom Oliver (Supervisor)