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

TL;DR

This study revises benchmarks and reveals that dispersion interactions are more crucial than exchange effects in accurately modeling halogen-bonding energies, supported by extensive SAPT analysis and corrected reference data.

Contribution

It provides a revised benchmark set for halogen bonds and demonstrates the dominant role of dispersion over exchange in energy calculations, challenging previous assumptions.

Findings

Dispersion effects are more significant than exchange in halogen-bonding energies.

Corrected inconsistencies in the XB51 benchmark set.

Dispersion corrections improve DFT predictions even with non-empirical exchange tuning.

Abstract

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 non-empirically 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 (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/parameterizing new DFT functionals specifically for complex halogen-bonding interactions.