Effects of ion–water Lennard-Jones potentials on the hydration dynamics around a monovalent atomic ion in molecular dynamics simulations

ABSTRACT

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 (r_MO), 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 r_MO) were artificially correlated in the MD simulations.

KEYWORDS:

• Hydration dynamics
• ion–water interaction
• empirical force field
• ion solvation
• molecular dynamics

Acknowledgements

We thank Daigo Itsuji (College of Life Sciences, Ritsumeikan University) for data preparation. This work was supported by the Japan Society for the Promotion of Science KAKENHI, Grant-in-Aid for Young Scientists (Grant Number: JP16K18526). The computational resources were provided by the HPCI System Research Project (Project IDs: hp180050, hp180054, hp190017, and hp190018), ROIS National Institute of Genetics, Japan, and Research Center for Computational Science, Okazaki, Japan.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Kota Kasahara http://orcid.org/0000-0003-0207-6271

Additional information

Funding

This work was supported by Japan Society for the Promotion of Science: [Grant Number JP16K18526].