Molecular Insights into the Influence of Ions on Water Structure. II. Halide Ions in Solution

Understanding how halide ions affect the structure and dynamics of water at the molecular level is essential for a wide range of chemical, biological, and environmental processes. In this study, we use molecular dynamics simulations with MB-nrg data-driven many-body potential energy functions to investigate the hydration properties of halide ions in bulk water. The results reveal distinct trends in hydration structure, residence times, dipole moment distributions, and infrared spectral signatures, reflecting variations in ion size, charge density, and polarizability. In particular, fluoride promotes uniquely strong and more directional hydrogen bonds with the surrounding water molecules, which leads to substantial spectral shifts and slower water exchange dynamics. In contrast, heavier halides induce only minimal perturbations on the water hydrogen-bond network, even within the first hydration shell. These insights provide a quantitative framework for understanding ion-specific effects in aqueous systems and set the stage for future studies of more complex environments such as aqueous interfaces and confined systems.