| Abstract: | A promising new method for optimizing molecular structures is described. In place of the terms involving bond angles and torsion angles, used in the force fields of conventional molecular mechanics, two-body central forces between atoms are used exclusively, resulting in a considerable computational advantage. The program STRFIT, using this method has been tested by comparing geometries obtained with those found using the popular molecular mechanics program MM2 (Allinger) for a variety of cyclic and acyclic molecules. For unstrained molecules, the difference in steric energy between geometries refined by STRFIT and MM2 is only a few tenths of a kilocalorie and up to about a kilocalorie for strained molecules. Geometry optimization with STRFIT, to a structure that is slightly higher in energy than the structure arrived at by MM2 starting from the same initial starting geometry, is three to eight times faster. A complete new package of programs for conveniently and rapidly doing molecular mechanics calculations is described. It includes a convenient algorithm for the input of approximate molecular structures, a rapid structure-optimizing module using a pure Central force-field approach, and a drawing program designed for use with a dot-matrix printer or a laser printer. |
