MMFF VII. Characterization of MMFF94, MMFF94s, and other widely available force fields for conformational energies and for intermolecular-interaction energies and geometries.

This article provides extensive comparisons for the MMFF94, MMFF94s, CFF95, CVFF, MSI CHARMm, AMBER*, OPLS*, MM2*, and MM3* force fields to experimental and high-quality ab initio data for conformational energies and to scaled ab initio data for hydrogen-bonded complexes. Some comparisons are also presented for CHARMM 22. The tests of conformational energies consisted of two sets of comparisons to experiment and one more extensive set of comparisons to relatively high-quality ab initio data. As in the derivation of MMFF94, scaled HF/6-31G* energies and geometries were used to assess the reasonableness of the calculated intermolecular interaction energies and geometries. The comparisons for intermolecular interactions appear to be the first broadly based comparisons to appear in the chemical literature. Taken together, the comparisons reveal that most of the force fields make sizable errors and frequently produce qualitatively incorrect results for both conformational and intermolecular-interaction energies. For example, three of the force fields produce individual errors in conformational energy of more than 10 kcal/mol, and four rate thiophene as a stronger hydrogen-bond acceptor than ammonia. Only MMFF94 and MMFF94s perform consistently well. Some MMFF deficiencies are apparent, however, particularly for conformational energies of halocyclohexanes. These deficiencies, and others recently found for condensed-phase simulations, will need to be addressed in any future reparameterization of MMFF. The quantum-chemical data used in this work have been placed on the Computational Chemistry List web site. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 730-748, 1999.