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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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           Better, faster descriptions of molecular interactions 
                      for computer simulations

                             Steven Rick

                  Advanced Biomedical Computing Center
                National Cancer Institute, Frederick, MD 

    Simulating chemical and biological systems on a computer requires
a description of the intermolecular interactions.  Arbitrarily accurate 
interactions can be calculated by numerically solving Schroedinger's 
equation. However, these ab initio methods are too computationally time 
consuming to be used for the large systems and long simulation times 
necessary for many of the systems chemists and biologists are interested 
in.  Most simulations of this type are done using empirical potential 
energy functions, which are parameterized to reproduce experimental or 
ab initio data and are relatively inexpensive to compute.  An important 
feature these potentials usually lack is polarizability, the electronic 
response to the electric fields of other molecules. Two methods for 
introducing polarizability into the existing potentials, and which bridge 
the gap between ab initio and empirical methods, will be presented. Both 
approaches let the properties of the potentials which are normally held 
constant (such as atomic partial charges or the bonded interactions) 
become variables and both preserve the speed of the empirical potential 
approaches.  One method is the fluctuating charge method (J. Chem. Phys., 
p. 6141, 1994) and its applications to water, ice and aqueous solutions 
will be discussed with an emphasis on the importance of polarizability 
for condensed phase systems. The other method has recently been developed 
for simulating proteins and its application to protein folding dynamics 
will be presented.

                          Monday , March 6, 2000
                                  4:30 pm
                        Room 206, Science & Tech. I

Refreshments will be served.
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Find the schedule at http://csi.gmu.edu/lcdm/seminar/schedule.html