| Research Projects Supported by HKU's High Performance Computing Facilities |
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| Researcher: |
| Dr GuanHua Chen, Department of Chemistry |
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| Project Title: |
| 1. Low-lying
Excited States of Light-Harvesting System II in Rs. Molischianum 2. Electronic and Tribological Properties of Carbon Nanotube Based Structures |
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| Project Description: |
| 1. The
Light-Harvesting system II (LHII) from Rs. molischianum is a circular
aggregate. It is composed of 8 weakly coupled bacteriochlorophyll-a (BChl-a)
in the upper ring (B800) and 16 strongly coupled BChl-a in the lower ring
(B850). Due to their large sizes, no calculation has been performed to solve
the electronic structures of the complete rings explicitly. We employ the
INDO/S-LDM method to calculate the absorption spectrum of each ring and
report the calculated results of thee BChl-a monomer, BChl-a dimers, and
entire B800 and B850 rings. 2. We have investigated the optical, electronic and mechanical properties of a series of carbon nanotube based structures. The optical properties of carbon nanotubes (CNTs) can be understood via a simple graphic analysis. A quantum mechanical simulation has been carried out to examine the field emission mechanism under a realistic experimental environment. Friction in CNT based oscillators is investigated via molecular dynamics simulation. |
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| Project Duration: |
|
1-2 years |
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| Project Significance: |
| 1. The basic
energy source for virtually all organisms is photosynthesis by which green
plants and other organisms use the energy of light to convert carbon dioxide
and water into simple sugar. Through the studies, we have better
understanding of the light harvesting mechanisms and the energy transfer
within the photosynthetic systems. 2. Multiwalled carbon nanotubes had been proposed as candidates for nanoscale molecular bearings, oscillators and tip for STM. Through the studies, we provide an understanding of electronic properties, nanoscale motion induced heating mechanisms and to propose means for reducing frictional effects. |
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| Results Achieved: |
| 1. The
absorption spectra of thee BChl-a monomer, BChl-a dimers, and entire B800
and B850 rings are calculated. It is found that the electron-hole pair is
mainly localized in one BChl-a with slight leakage to its nearest neighbors.
It is further shown that the INDO/S-LDM method is capable of calculating
very large electronic structures. Ng MF, Zhao Y, Chen GH, J.Phys.Chem B, 107, 9589 (2003). 2. a) It is found that a rocking motion is responsible for significant phonon energy acquisitions. For oscillators with long nanotubes translational energies are mainly dissipated via a wavy deformation in the outer tube undergoing radial vibrations. Frictional forces between 10¡V17 and 10¡V14 N per atom are found for various dissipative mechanisms. Zhao Y, Ma CC, Chen GH, Jiang Q, Phys. Rev. Lett. 91, 175504, (2003) b) Unconventional nature of CNT field emission mechanism is revealed. The potential barrier height is found to be a nonlinear function of the applied field, and is system-dependent. It is proposed that through modification of the tip it may lead to drastic alternation of emission current or threshold voltage. Zheng X, Chen GH, Li Z, Deng S, Xu N, Phys. Rev. Lett. (accepted). |
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| Remarks on the Use of High Performance Computing Cluster: |
|
The HPC Cluster provides us the computer resource which greatly reduces the CPU time in the calculations. |
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| Email Address: |
| ghc@everest.hku.hk |
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