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Ab initio Semiclassical Initial Value Representation: Development of New Methods Open Access


Other title
ab initio
molecular dynamics
quantum dynamics
vibrational states
electronic structure
vibrational energies
semiclassical initial value representation
classical mechanics
direct dynamics
semiclassical dynamics
Type of item
Degree grantor
University of Alberta
Author or creator
Wong, Stephanie Y Y
Supervisor and department
Brown, Alex (Chemistry)
Roy, Pierre-Nicholas (Chemistry)
Examining committee member and department
Geva, Eitan (Chemistry, University of Michigan)
Campbell, Robert (Chemistry)
Klobukowski, Mariusz (Chemistry)
Klassen, John (Chemistry)
Department of Chemistry

Date accepted
Graduation date
Doctor of Philosophy
Degree level
Between the world of classical and quantum mechanics there lies a region where both are used to provide an accurate (quantum) but computationally tractable (classical) description of motion: semiclassical mechanics. The heart of semiclassical theory is the use of the classical path (or, alternatively, the classical trajectory), in a way to elucidate quantum mechanical properties. At the heart of this theory is the semiclassical expression of the quantum mechanical propagator: e^{-iHt/h_bar}. By reexpressing the propagator in semiclassical form (specifically, the Herman-Kluk initial value representation), we are able to use classical trajectories to determine the vibrational energies of molecules. We first develop the software tools for ab initio molecular dynamics in MMTK. In the process of doing so, we have examined the ground and excited state dynamics of the methyl hypochlorite CH3OCl molecule. Vertical excitation energies and transition dipole moments are calculated at the complete active space self-consistent field (CASSCF)/6-31+G(d) level of theory. With these proven tools, the semiclassical initial value representation (SC-IVR) method for the calculation of vibrational state energies is implemented into this framework. This is the main focus of the thesis. A thorough analysis of the vibrational energies for some of the fundamental, overtone and combination modes of H2CO is completed. Then, the time-averaged variant of SC-IVR is implemented on the same molecular system. Through this study, we have discovered many caveats of SC-IVR calculations which we discuss. We have shown that ab initio SC-IVR is a useful method to calculate vibrational energies and that its values approach that of quantum mechanical methods such as vibrational self-consistent field (VSCF) and vibrational configuration interaction (VCI).
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
S.Y.Y. Wong, P.-N. Roy and A. Brown, Canadian Journal of Chemistry, 87 1022 (2009)S. Y. Y. Wong, D. M. Benoit, M. Lewerenz, A. Brown, and P.-N. Roy, J. Chem. Phys. 134 094110 (2011)

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