Anisotropic Repulsion Potentials for Cyanuric Chloride (C₃N₃Cl₃) and Their Application to Modeling the Crystal Structures of Azaaromatic Chlorides

A series of nonempirical intermolecular potentials has been developed for the cyanuric chloride dimer, using the overlap model to determine the anisotropy of the repulsive wall around each atom. Calibration against intermolecular perturbation theory calculations enables the penetration and charge-transfer energy to be explicitly included with the exchange-repulsion to give a simple repulsion model in an anisotropic atom-atom form. These model repulsion potentials are used in conjunction with an atomic multipole electrostatic model and an atom-atom dispersion model to give nonempirical potential models, which are tested for their ability to reproduce the crystal structure of cyanuric chloride. The best nonempirical potential is successfully used to construct a simpler transferable model for closely related azaaromatic chlorides. The nonempirical potential reproduces the experimental space group of cyanuric chloride, unlike some empirically fitted repulsion-dispersion potentials. This first nonempirical repulsion potential to model the polar flattening of Cl atoms also reproduces the N . . . Cl and Cl . . . Cl interactions in other crystal structures.