Development of a novel ReaxFF reactive potential for organochloride molecules

Abstract

This article presents a new reactive potential in the ReaxFF formalism. It aims to include the chlorine element, and opens up the fields of use of ReaxFF to the whole class of organochloride compounds including conjugated or aromatic groups. Numerous compounds in this family raise global awareness due to their environmental impact, and such a reactive potential will help investigate their degradation pathways. The new force field belongs to the aqueous branch. The force field parameters were fitted against high-level quantum chemistry calculations, including CASSCF/NEVPT2 calculations and density functional theory calculations, and its accuracy was evaluated using a validation set. The root means square deviation against quantum mechanics energies is 0.38 eV (8.91 kcal/mol). From a structural point of view, the root means square deviation is about 0.06Å for the bond lengths, 11.86{degree sign} for the angles and 4.12{degree sign} for the dihedral angles. With CHONCl-2022_weak new force field, we successfully investigated the regioselectivity for nucleophilic or electrophilic attacks on polychlorinated biphenyls (PCB), which are toxic and permanent pollutants. The rotation barriers along the bond linking the two benzene rings, which is crucial in the toxicity of these compounds, are well reproduced by CHONCl-2022_weak. Then our new reactive potential is used to investigate the chlorobenzene atmospheric oxidation, initiated by a hydroxyl radical. The reaction pathways computed with ReaxFF agree with the quantum mechanics results. We showed that, in the presence of dioxygen molecules, the oxidation of chlorobenzene likely leads to the formation of highly oxygenated compounds after the abstraction of hydrogen radicals.