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    COLLOQUIUM OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS
        Institute for Computational Sciences and Informatics
	                      CSI 898-Sec 001  
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      The Density-Functional based Tight-Binding method (DF-TB):
                         Polymerized C_60 clusters.

                             Dirk Porezag
               Naval Research Laboratory, Washington, DC

     Traditional tight-binding theory may be seen as a first-order 
  approximation of density-functional theory if one applies the 
  latter formalism to determine total energy changes induced
  by small electron density variations. I will show that it is possible 
  to use this idea for the construction of realistic tight-binding
  total energy models that can be used in large-scale condensed matter 
  simulations. As an example, results for structure, energetics, and 
  vibrations of C_60 oligomers will be presented. The properties of 
  these systems have been investigated very thoroughly in the last few
  years since it was discovered that ultraviolet light causes the
  C_60 clusters to form covalent intramolecular bonds. I will
  demonstrate that the computer simulations perfomed for these systems 
  may be used to identify the correlations between experimental
  conditions and resulting material.
     Finally, I will introduce an improvement of the DF-TB method 
  which also includes second-order effects in the above mentioned
  approximation of density-functional theory. These contributions
  are essential if the charge states of the different atomic constituents
  in a condensed matter system differ significantly from the free 
  neutral atom.
                         Monday, February 9 1998
                                 4:30 pm
                        Room 206, Science & Tech. I

Refreshments will be served.
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(http://www.csi.gmu.edu/lcdm/seminar/schedule.html)