Molecular Modeling and Small-Molecular Crystal Structures From Powder Data. Clive M. Freeman and Alan M. Gorman, Molecular Simulations Inc., 9685 Scranton Road, San Diego, CA 92121

Molecular simulation techniques are assuming an increasing role in structure solution and refinement. A suite of computational techniques, ranging from model construction to automated solution procedures, and their application to molecular structure determination will be described. In addition to providing familiar building and visualization capabilities, contemporary computational methods permit structure regularization, cell and symmetry analysis, and property simulation capabilities which extend dramatically the scope of traditional model building. Interactive computational techniques are particularly valuable in coupling related crystallographic knowledge and the structure solution process, in model manipulation, and in the visualization of Fourier and difference Fourier maps. Such discrete simulation capabilities can be combined with diffraction simulation, permitting real time evaluation of developing models. Automated procedures for packing analysis and simulated annealing in structure solution will be described.