title: Halogen Bonding from Dispersion-Corrected Density-Functional Theory: The Role of Delocalization Error.
abstract: Halogen bonds are formed when a Lewis base interacts with a halogen atom in a different molecule, which acts as an electron acceptor. Due to its charge transfer component, halogen bonding is difficult to model using many common density-functional approximations because they spuriously overstabilize halogen-bonded dimers. It has been suggested that dispersion-corrected density functionals are inadequate to describe halogen bonding. In this work, we show that the exchange-hole dipole moment (XDM) dispersion correction coupled with functionals that minimize delocalization error (for instance, BH&HLYP, but also other half-and-half functionals) accurately model halogen-bonded interactions, with average errors similar to other noncovalent dimers with less charge-transfer effects. The performance of XDM is evaluated for three previously proposed benchmarks (XB18 and XB51 by Kozuch and Martin, and the set proposed by Bauzá et al.) spanning a range of binding energies up to ∼50 kcal/mol. The good performance of BH&HLYP-XDM is comparable to M06-2X, and extends to the "extreme" cases in the Bauzá set. This set contains anionic electron donors where charge transfer occurs even at infinite separation, as well as other charge transfer dimers belonging to the pnictogen and chalcogen bonding classes. We also show that functional delocalization error results in an overly delocalized electron density and exact-exchange hole. We propose intermolecular Bader delocalization indices as an indicator of both the donor-acceptor character of an intermolecular interaction and the delocalization error coming from the underlying functional.
authors.affiliation: National Institute for Nanotechnology, National Research Council of Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Otero-de-la-Roza
authors.affiliation: Chemistry and Chemical Biology, School of Natural Sciences, University of California , Merced, 5200 North Lake Road, Merced, California 95343, United States.
authors.forename: Erin R
authors.initials: ER
authors.lastname: Johnson
authors.affiliation: National Institute for Nanotechnology, National Research Council of Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada.|Department of Chemistry, University of British Columbia , Okanagan, Fipke Center 357, 3247 University Way, Kelowna, British Columbia V1V 1V7, Canada.
authors.forename: Gino A
authors.initials: GA
authors.lastname: DiLabio