Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session D38: Focus Session: The Chemical Physics of Biological and Biologically-inspired Solar Energy Harvesting III |
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Sponsoring Units: DCP Chair: Martin Plenio, Imperial College Room: 410 |
Monday, March 16, 2009 2:30PM - 3:06PM |
D38.00001: Exciton migration and fluorescence quenching in photosystem II Invited Speaker: When exposed to excess light illumination photosynthetic organisms switch into a photoprotective quenched state where the excess energy is safely dissipated as heat. It was recently discovered that the main light-harvesting complex of plants, LHCII, plays a key role in the dissipation of excess energy. Here we demonstrate that the excitation kinetics in the quenched state can be described by a simple model, which assumes specific trapping centers to be present in the system [1]. In order to explain the experimental results exciton-exciton annihilation is taken into account. To verify the effectiveness of the non-photochemical quenching center, possessing a short lifetime, in preventing the excess excitations from reaching the reaction center, the studies of the excitation quenching depending on positioning and origin of the quencher in the antenna complexes are also considered. \\[4pt] [1] N. E. Holt, D. Zigmantas, L. Valkunas, X.-P. Li, K. K. Niyogi, G. R. Fleming, \textit{Science} 307, 433 (2005). [Preview Abstract] |
Monday, March 16, 2009 3:06PM - 3:42PM |
D38.00002: Environment-assisted quantum transport in photosynthetic complexes. Invited Speaker: Transport phenomena at the nanoscale are of interest due to the presence of both quantum and classical behavior. In this work, we demonstrate that quantum transport efficiency can be enhanced by a dynamical interplay of the system Hamiltonian with the pure dephasing dynamics induced by a fluctuating environment. This is in contrast to fully coherent hopping that leads to localization in disordered systems, and to highly incoherent transfer that is eventually suppressed by the quantum Zeno effect. We study these phenomena in the Fenna-Matthews-Olson protein complex as a prototype for larger photosynthetic energy transfer systems. We also show that disordered binary tree structures exhibit enhanced transport in the presence of dephasing. We address the question of the role of coherence in the energy transfer in the FMO complex and discuss details about the theoretical modeling of photosynthetic oomplexes and organic photovoltaic materials. [Preview Abstract] |
Monday, March 16, 2009 3:42PM - 3:54PM |
D38.00003: Engineering Efficient Exciton Energy Transfer in Artificial Arrays Leslie Vogt, Alejandro Perdomo, Semion Saikin, Alan Aspuru-Guzik A critical component of light harvesting devices is efficient transfer of excitonic energy. Biological systems have optimized this process over time for the particular molecular components involved. Understanding this energy transfer in model arrays will allow us to engineer new materials for solar cell technology. In particular, we explore a perturbative approach to optimize both coherent and incoherent transport in small arrays. By following the evolving coherences and populations over time using a density matrix formalism, we gain an intuition about the importance of coherent processes in exciton transfer in natural and designed light harvesting systems. [Preview Abstract] |
Monday, March 16, 2009 3:54PM - 4:06PM |
D38.00004: Coherent Excitonic Transfer in the Fenna Matthews Olson Complex Gregory Engel Evidence for a purely quantum mechanical mechanism of energy transfer in photosynthetic complexes was discovered in the Fenna-Matthews-Olson complex of \textit{Chlorobium tepidum in 2007}. The quantum beating phenomenon observed in this complex is now much better understood. Specifically, detailed, testable microscopic models for the mechanism of this energy transfer have emerged, and precise quantum dynamical models now predict that this mechanism accounts for approximately one quarter of the energy transferred at room temperature. Further, new data indicate that this mechanism is not specific to FMO, but manifests in reaction centers of purple bacteria and antenna complexes of higher plants. A new experimental effort to observe quantum coherence at room temperature will be discussed. Specifically, by comparing population transfer rates and coherence transfer quantum beating signals, we caluclate the fraction of the energy moving through the wave-like mechanism. Further, by studying the temperature dependence of the energy transfer, we elucidate the microscopic mechanism for wavelike energy transfer and be able to comment on the robustness of the mechanism. Are light harvesting proteins delicately ``tuned'' by evolution to support coherence transfer or should any proteinaceous environment support this mechanism? Details of the experimental apparatus, results and future experiments will be presented. [Preview Abstract] |
Monday, March 16, 2009 4:06PM - 4:18PM |
D38.00005: Excitation transport in open quantum systems: the role of environmental correlations. Mohan Sarovar, Yuan-Chung Cheng, Birgitta Whaley The recent discovery of quantum coherent phenomena in photosynthetic complexes [Engel et.al., Nature, 446, 782 (2007), Lee et. al., Science, 316, 1462 (2007)] has prompted several studies into the efficiency of transport processes in open quantum systems. Several of these studies have revealed a subtle interplay between coherent and decoherent dynamics in the overall efficiency of transport in these open systems. Some have shown that decoherence can improve efficiency. However all studies have used simple uncorrelated models of decoherence that are not accurate for photosynthetic complex environments, which are known to be spatially and temporally correlated. In this work we investigate the role of environmental correlations in quantum transport in open systems and show that the exact nature of the correlations can have a large impact on the efficiency of energy harvesting. We illustrate our results using the Fenna-Matthews-Olsen photosynthetic complex. [Preview Abstract] |
Monday, March 16, 2009 4:18PM - 4:30PM |
D38.00006: Local Correlation Calculations Using Standard and Renormalized Coupled-Cluster Methods Piotr Piecuch, Wei Li, Jeffrey Gour Local correlation variants of the coupled-cluster (CC) theory with singles and doubles (CCSD) and CC methods with singles, doubles, and non-iterative triples, including CCSD(T) and the completely renormalized CR-CC(2,3) approach, are developed. The main idea of the resulting CIM-CCSD, CIM-CCSD(T), and CIM-CR-CC(2,3) methods is the realization of the fact that the total correlation energy of a large system can be obtained as a sum of contributions from the occupied orthonormal localized molecular orbitals and their respective occupied and unoccupied orbital domains. The CIM-CCSD, CIM-CCSD(T), and CIM-CR-CC(2,3) algorithms are characterized by the linear scaling of the total CPU time with the system size and embarrassing parallelism. By comparing the results of the canonical and CIM-CC calculations for normal alkanes and water clusters, it is demonstrated that the CIM-CCSD, CIM-CCSD(T), and CIM-CR-CC(2,3) approaches recover the corresponding canonical CC correlation energies to within 0.1 {\%} or so, while offering savings in the computer effort by orders of magnitude. By examining the dissociation of dodecane into C$_{11}$H$_{23}$ and CH$_{3}$ and several lowest-energy structures of the (H$_{2}$O)$_{n}$ clusters, it is shown that the CIM-CC methods accurately reproduce the relative energetics of the corresponding canonical CC calculations. [Preview Abstract] |
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