Halogen Bonding Interactions: Revised Benchmarks and a New Assessment of Exchange vs Dispersion

We
present a new analysis of exchange and dispersion effects for calculating
halogen-bonding interactions in a wide variety of complex dimers (69
total) within the XB18 and XB51 benchmark sets. Contrary to previous
work on these systems, we find that dispersion plays a more significant
role than exact exchange in accurately calculating halogen-bonding
interaction energies, which are further confirmed by extensive SAPT
analyses. In particular, we find that even if the amount of exact
exchange is nonempirically tuned to satisfy known DFT constraints,
we still observe an overall improvement in predicting dissociation
energies when dispersion corrections are applied, in stark contrast
to previous studies (Kozuch, S.; Martin, J. M. L. J. Chem. Theory Comput. 2013, 9, 1918−1931). In addition to these new analyses, we correct several (14) inconsistencies
in the XB51 set, which is widely used in the scientific literature
for developing and benchmarking various DFT methods. Together, these
new analyses and revised benchmarks emphasize the importance of dispersion
and provide corrected reference values that are essential for developing/parametrizing
new DFT functionals, specifically for complex halogen-bonding interactions.