Nonbonded potential parameters were derived from the crystal structures of five perchlorohydrocarbons. Intermolecular interactions were represented by interatomic (exp-6-1) nonbonded potential functions. Optimized values for the nonbonded potential parameters were obtained by four different methods. These methods are: direct fit to structural parameters; Taylor's series approximation for direct fit; force minimization with diagonal-weight matrix; and force minimization with full-weight matrix. The direct fit to structural parameters method gave the best results but was expensive of computer time. The Taylor's series approximation for direct fit method was satisfactory. The force minimization with diagonal weights method gave poor results. Force minimization with full weights was the best of the approximation methods, and was almost as good as the direct-fit method. The transferability of the nonbonded potential parameters among the five compounds was established within threshold error limits. Anisotropic potential functions for chlorine, which have been suggested by other workers for the polymorphic 1,4-dichlorobenzene crystal structures, were not found necessary to achieve threshold fits to these perchlorohydrocarbon structures.
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HSU et al. (1980) studied this question.