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Book: Quantum Dynamics: Application in Biological and Materials
Systems by Eric R. Bittner
Even though time-dependent spectroscopic techniques continue to push
the frontier of chemical physics, they receive scant mention in
introductory courses as they are poorly covered in standard
texts. This text bridges the gap between what is traditionally taught
in a one-semester quantum chemistry course and the modern field of
chemical dynamics. It provides needed background in quantum mechanics
and then discusses theory and a number of applications that are of
current interest, from molecular electronics to
photosynthesis. Written in a pedagogic style, it details needed
computational components and sample calculations using Mathematica.
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I am primarily interested in the dynamics of molecules in their excited electronic states.
We use both computational and theoretical approaches to answer the following questions:
- Which nuclear motions are responsible for accommodating the
energetics of the transition by either absorbing excess energy in an
exothermic transition or supplying the energy deficit in an
- What is the role of quantum coherence, localization, and relaxation
in determining not only the transition rates, but also the
transport, and spectroscopic properties of excitonic and charge-transfer states,
especially in organic semiconducting systems?
- How do these effects affect the observed dynamics, material properties, or
electronic behavior in systems such as organic light-emitting diodes,
photovoltaic cells, and DNA chains.
Model excited state potential energy surfaces for
along the proton transfer coordinates for a stacked dAdT pair.
Some Recent Seminars (in PDF)
- Excitons in DNA (July 08)
- Optical Electronic Group Meeting, 15-October-2007
- Cambridge Chemistry Seminar 10-Oct-2007
- OE Seminar 16-October 2007
Exciton Dynamics in Conjugated Polymers
Organic semiconductors are quite different than
their inorganic counter parts in that most of their electronic
properties are determined by local molecular electronic interactions
rather than by delocalized states. The impact of local level
interactions is driven home at the interface between domains of
semiconducting polymers in which there is an off-set between the
respective HOMO and LUMO orbital energies. Here
our work has largely focused upon developing robust semi-empirical
descriptions of charge and energy transfer between co-facially stacked
conjugated polymers. One distinguishing aspect of our work is that we
have focused upon how the electronic dynamics are modulated and tuned
by the intramolecular vibrational motions of the polymers. Typically,
this is accomplished within the Marcus-Hush approach; however, we
showed recently that when the non-adiabatic coupling is sufficiently
strong, such approaches can give quite different relaxation pathways
than if the explicit vibrational coordinate dependence in the coupling
is included. My group has also developed a new time-convolutionless
approach for including non-Markovian vibrational dynamics into the
calculation of phonon-driven electronic transition probabilities.
Lastly we have begun to explore a projection operator approach for
determining sub-sets of phonon modes that are mostly responsible for
the tuning, coupling, and energetic accommodation of electronic
Energy transport and relaxation in DNA
The electronic transport properties of DNA has attracted considerable
attention over a number of years.
The possibility that
electron transfer in DNA chains may be linked to several biological
processes has spurred nearly countless experimental and theoretical studies.
From a biophysical standpoint,
DNA also has a remarkably large photo-absorption cross-section for UVB (290-320 nm)
light, making it susceptible to carcinogenic mutations.
With this in mind, is important to understand how excitation energy is transported
along the chain, the role of intra-strand stacking effects and interstrand couplings.
Our guiding principle in this is that the interbase electronic interactions
are modulated by the global structural dynamics, but that the DNA molecular dynamics
are not affected by the excited states. Thus, we can bring to bear an arsinal of
computational and theoretical tools ranging from molecular dynamics and TD-DFT to analytical
lattice models to develop a complete theoretical understanding of this system.
Quantum dynamics of small clusters
We have recently developed a novel quantum hydrodynamic based approach for computing the
quantum vibrational energies of small atomic clusters. Our numerical approach combines a
a de Broglie/Bohm description of the quantum equations of motion with a Baysian sampling algorithm
for the atomic density function. We are currently usig this approach to study quantum contributions
to the thermodynamics of small rare gas clusters (Ne)n especially in thermal regions close to the
bulk melting transition.
Supersymmetry and Supersymmetric Quantum Mechanics
Supersymmetry (SUSY) was originally posed as a fundimental symmetry
that relates a particle of one spin to a particle whose spin differs
by 1/2 hbar. These are known as super-partners. In essence, for
every boson, there is a corresponding fermion with the same mass
(energy). To date, this has not been observed and so supersymmetry
must have been spontaneously broken at some point and may possible
exist at the TeV energy scale.
SUSY-quantum mechanics, on the other hand uses the basic idea of SUSY
and quantum groups to relate the spectra and states of a system to one
Hamiltonian (H1) to a partner system (with H2)
in which every state has a partner except the ground state. We have
recently used SUSY quantum mechanics to develop a technique for
computing excitation energies for model quantum systems using only
input from a ground-state Monte Carlo calculation. This is exciting
new development which we are carefully examining and extending in a
Selected Publications from Mendeley
Click Here for
Complete bibliography and Reprints
Eric Bittner is a member of Chemistry on Mendeley.