A Failure of DFT Is Not Necessarily a DFT Failure-Performance Dependencies on Model System Choices

The claim that DFT does not provide an accurate description of a weak Ru-C interaction (J. Chem. Theory Comput.2007, 3, 665-670) is put into broader perspective. The mismatch between structures obtained from DFT (BP86) as well as DFT-D (BP86-D2) calculations of isolated molecules in the gas phase and geometries resulting from X-ray crystal structure determination is due to a dissatisfactory chemical model system. Intermolecular forces within the molecular surroundings of the crystal obtained from semiempirical lattice energy calculations emerge as likely candidates responsible for the incongruity of experimental results and computation.