  Halogen bonding has emerged as an important noncovalent interaction in a
myriad of applications, including drug design, supramolecular assembly, and
catalysis. Current understanding of the halogen bond is informed by electronic
structure calculations on isolated molecules and/or crystal structures that are
not readily transferable to liquids and disordered phases. To address this
issue, we present a first-principles simulation-based approach for quantifying
halogen bonds in molecular systems rooted in an understanding of nuclei-nuclei
and electron-nuclei spatial correlations. We then demonstrate how this approach
can be used to quantify the structure and dynamics of halogen bonds in
condensed phases, using solid and liquid molecular chlorine as prototypical
examples with high concentrations of halogen bonds. We close with a discussion
of how the knowledge generated by our first-principles approach may inform the
development of classical empirical models, with a consistent representation of
halogen bonding.
