The Interaction of Small Molecules and Short Intense Laser Fields

Abstract

The advent of short intense laser fields promises unprecedented quantum control over chemical reactions. Laser fields of femtosecond duration are now readily available on the tabletop. In this dissertation we investigate the interaction of these laser fields with small molecules through simulations using the time-dependent density-functional theory (TDDFT) coupled with the Ehrenfest dynamics. We also investigate time propagation algorithms to improve the computational efficiency of solving the time-dependent Kohn-Sham equations of the TDDFT. In particular we construct the time propagator with two subspace methods, using either the Lanczos basis or the eigenbasis of the Kohn-Sham Hamiltonian, and compare the accuracy and computational efficiency of these methods to the highly accurate fourth-order Taylor expansion of the propagator. In the application of the simulations we consider a range of laser durations and intensities, the effects of molecular alignment, the coupling of the dynamics between the electrons and the nuclei, and the role of electronic excitation. The systems examined are acetylene (C2H2) and ethylene (C2H4) interacting with linearly polarized pulses, and circularly polarized pulses interacting with acetylene and the hydrogen molecule (H2).