A computational modelling study of chlorine dioxide and its role in water purification cycles

Abstract

This study involves the computational investigation into the perceived reactivity of a group of sixty (60) sub- and extended- chlorine oxide species with the general formulae of CℓxOy applied to water purification. In order to achieve the ultimate objective of elucidating their chemical role in aqueous media, acting as oxidative agents, an intensive computational approach has been followed to determine their thermochemical properties. The extended species of CℓO2 display a complex sequence of bonding character with an appreciable charge dissipation (extracted as partial charges), which complicates the effective selection of basis sets and electronic structural optimization, during Ab Initio analyses. Besides a single molecular computational analysis, an alternative grand canonical ensemble approach was introduced, applying Gibbs ensemble Monte Carlo simulations, supported by revised force field parameters to derive at optimum model sizes. In this context, this approach proved highly efficient, resulting in consistent thermochemical properties for all species, through optimum selection of Hamiltonians and appropriate basis sets, during quantum chemical analyses. Excellent correlations with published Heat of Formation energies were obtained for almost all the ensemble derived species. A few energy discrepancies identified during Ab Initio (VASP and Gaussian software) calculations will need to be investigated more thoroughly in a further study. Chemical structure geometries were typically maintained for all models and self-consistency reached in all the quantum chemical refinement cycles. Some of these species are presented as radical and ionic entities, which complicates their quantum atom potential representations. This observation specifically applies to species exhibiting variable spin conditions. This spin variability can further promote spin contamination, through extensive polarization contributions. Charged species were unfortunately not exposed to empirical ensemble simulations (reasons given) and had to be considered as single molecular entities