This work was supported by the Division of Chemical Sciences;
Office of Basic Energy Sciences;
U.S. Department of Energy. Computations reported in this work were performed on IBM RS/6000 in the Computational Laboratory for Environmental Biotechnology in the Department of Chemical Engineering at the University of Virginia;
and on the IBM SP/2 of the Computing and Administrative Systems at the University of Tennessee. The IBM SP/2 was obtained under the IBM Shared University Resource program;