A Concise Set of “Large”, Symmetric Molecules for Evaluation of Modern Computational Methods

The structures of a series of strained in -cyclophanes, for which good X-ray data are available, were calculated by using a variety of ab initio and hybrid density functional (HDFT) methods. The HDFT methods were found to overestimate systematically the transannular nonbonded contact distances in these molecules. A consideration of the deficiencies of existing test sets for the evaluation of modern computational methods led to the compilation of a set of larger molecules with accurately known geometries. Twenty highly symmetric molecules were selected for which there exist high-quality X-ray structures where the molecules reside at high symmetry sites with only relatively weak intermolecular interactions. The experimental structures of these molecules were compared with the structures calculated by five computational methods [HF/3-21G(*), MP2(FC)/6-31G(d), B3LYP/6-31G(d), B3PW91/6-31G(d), and B3PW91/cc-pVDZ], and the results are discussed in the context of choosing computational methods for routine geometry optimizations.