QM/MM MD Simulations of Iodide Ion (I−) in Aqueous Solution: A Delicate Balance between Ion−Water and Water−Water H-Bond Interactions

The characteristics of an iodide ion (I−) in aqueous solution were investigated by means of HF/MM and B3LYP/MM molecular dynamics simulations, in which the ion and its surrounding water molecules were treated at HF and B3LYP levels using the LANL2DZdp and D95 V+ basis sets for I− and water, respectively. According to both the HF/MM and B3LYP/MM results, the ion−water interactions are relatively weak, compared to the water−water hydrogen bonds, thus causing an unstructured nature of the hydration shell. Comparing the HF and B3LYP treatments for the description of this hydrated ion, the overestimation of the ion−water hydrogen-bond strength by the B3LYP method is recognizable, yielding a remarkably more compact and too rigid ion−water complex.