This thesis focuses on two of the most active fields of chemical physics. One is long-range charge transfer in complex molecular systems such as DNA, and another is quantum dissipation that is about the general theory of complex molecular system....[ Read more ]

This thesis focuses on two of the most active fields of chemical physics. One is long-range charge transfer in complex molecular systems such as DNA, and another is quantum dissipation that is about the general theory of complex molecular system.

Part I is on charge transfer in DNA molecules. Starting with the introduction of the standard electron transfer theory, we overview and summarize the current research status of charge transfer in DNA in both theory and experiment in Chapter 1. To build a bridge between theoretical calculations and experimental chemical yields, Chapter 2 presents a formulation based on a superexchange-mediated sequential hopping model. An exact mapping between the stationary chemical yields and the normalized electric currents is established, followed naturally by the Ohm's law for the kinetic multistep hopping processes. To determine the coherent unistep (superexchange) contributions, the scattering matrix technique is exploited. In order to examine the possibility and effects of partially incoherent tunneling in DNA systems, a generalized scattering matrix formalism is constructed in Chapter 3. This is a generalized Büttiker phase-breaking formalism that clearly elucidates the interplay of electron resonance, coherence, dephasing, inelastic scattering, and heterogeneity effects, which are known to be physically important in long range electron transfer/transport processes. Obtained is an analytical expression of partially incoherent tunneling probability in model donor-bridge-acceptor systems with arbitrary lengths and sequences. To take the effects of electronic structure and its incoherent interaction with aqueous solution into account, Chapter 4 gives a quantum chemistry based Green’s function formulation, and thus elucidates the mechanism of long-range charge transfer in DNA double helix at a microscopic level. Semiquantitive comparisons with experiments are also obtained.

Part II is about the development of quantum dissipation theory, together its application to a general topic of quantum stochastic resonance transport. After a general overview of the background knowledge in Chapter 5, a Liouville-space algebraic approach is exploited in Chapter 6 to revisit and further bridge between two most commonly used quantum dissipation theories, the Bloch-Redfield theory and Fokker-Planck equations. The nature of the common approximation scheme involving in these two theories is analyzed in detail. With the general theory built on a solid basis, the cooperative effects of driving and dissipation on transport in a model two-level system is then studied in Chapter 7. Analyzed in detail are the rate-matching and Rabi resonance conditions for the tunneling stochastic resonance. Large amplitude transport is found near not only the fundametal-harmonics region, but also higher harmonic resonance vicinities. Demonstrations are carried out to highlight the interplay between the strength of dissipation, and the intensity and frequency of external driving field.

Finally, we make a brief summary of this thesis research, followed by a discussion of future directions toward understanding structure dynamics correlation in complex molecular systems.