Effects of ion–water Lennard-Jones potentials on the hydration dynamics around a monovalent atomic ion in molecular dynamics simulations
The molecular dynamics (MD) method is a promising technique to dissect the atomistic details of water dynamics around a solute. However, the quantitative predictions of experimentally measured kinetic properties, e.g. translational diffusion coefficient (D) and rotational relaxation time (τ), are not straightforward. Current water models have failed to reproduce these properties quantitatively; therefore, the fine-tuning of water models is required. In this study, we examined the effects of ion–water Lennard-Jones (LJ) potentials on the water dynamics around a monovalent atomic ion. For the TIP5P water model, we introduced new LJ potentials for the ion–hydrogen and ion–pseudoatom interactions, which were zero in the original TIP5P model. The hydration properties, i.e. D, τ, and the radius of the first hydration shell (rMO), were examined for various parameter settings. As a result, the new parameters certainly improved the reproducibility of the hydration properties in correspondence with experimental values. However, it is still difficult to reproduce faster rotational relaxation of hydration water than that of bulk water. In addition, we found that the three hydration properties (D, τ, and rMO) were artificially correlated in the MD simulations.
