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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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           A New Class of Parallel Diffusion Algorithms

                         James A. Given
 
           Center for Advanced Research in Biotechnology and
          Biotechnology Division, NIST, Gaithersburg, Maryland  

We have previously used first-passage algorithms to treat random diffusion 
in a complex, two-phase environment. These algorithms utilize an efficient 
diffusion propagator selected from a library of Laplacian Green's functions 
in order to traverse, in a single propagation event, a large portion of 
the diffusing particle's environment which is known to be free of 
interaction sites. This approach was shown to provide the most rapid and 
accurate calculations currently available of translational hydrodynamic 
friction of an irregularly shaped object, e.g. a macromolecule. A similar 
algorithm calculates mutual capacitance; this is being used to calculate 
suspension rheology. In this talk, we introduce a powerful extension of
this class of algorithms: we show how to solve a general, stationary
Smoluchowski equation by shifting the force-field terms, i.e., all the
terms other than the Laplacian term, to the RHS and treating them as 
source terms to be determined self-consistently. These field-induced 
source terms then prescribe the rate at which diffusing particles are 
created at various points in the system. The newly-created particles 
subsequently undergo force-free diffusion in the environment, which we 
model with the original high-speed first-passage algorithm. In particular, 
we provide an efficient algorithm for calculating the solvation energy 
of a macromolecule. 

	               Monday , October 6 1997
                                 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)