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           COLLOQUIUM OF THE COMPUTATIONAL MATERIALS SCIENCE CENTER
                              College of Science
                       (CDS Department CSI 898-Sec 001)
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 From Oligomers to Polymers: Theoretical Studies of the Geometrical, 
  Electronic, and Vibrational Properties of Conjugated Systems

                           Shujiang Yang
           Computational Materials Science Center 
            George Mason University, Fairfax, VA 
Conjugation in extended systems gives rise to unique properties. For 
example, conjugated polymers possess unique combination of characteristics: 
electronic, optical, magnetic properties of semiconductors and metals; and, 
processing properties of plastics. Band gap control is essential in 
achieving those properties. Theoretical methods were first screened with 
available experimental data on conventional conjugated polymers and/or 
their oligomers, the validated methods were then used to predict and design 
various novel intrinsic low band gap conducting polymers, including various 
acetylenic coupled ladder polymers and aromatic-quinonoid copolymers. To 
accurately predict vibrational spectroscopy of extensively conjugated 
systems has been challenging to computational chemists due to the strong 
electron-phonon coupling in these systems. Currently available theoretical 
models are proved to be un-applicable for this matter, especially for the 
extremely conjugated system, polyyne. A novel linear/exponential hybrid 
force field scaling scheme is proposed in accompanying with quantum 
mechanical vibrational calculations to solve this problem. It has been 
successfully applied to polyyne and polyacetylene, and in principle can 
be extended to all extensively conjugated systems.

                        Monday, March 3, 2008
                                  4:30 pm
                     Room 301, Research I, Fairfax Campus

Refreshments will be served at 4:15 PM.
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Find the schedule at www.cmasc.gmu.edu/seminar/schedule.html
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