Systematic Evaluation of Ion Diffusion and Water Exchange

Area of Science:

• Computational chemistry
• Physical chemistry
• Chemical physics

Background:

• Diffusion is a fundamental fluid property with broad scientific and daily life applications.
• While liquid diffusion is well-studied, theoretical analysis of transition metal ion diffusion, especially radioactive ions, remains limited.
• This gap hinders reliable predictions for hazardous materials.

Purpose of the Study:

• To develop a computational workflow (ISAIAH) for accurate simulation of ion diffusion coefficients in water.
• To validate the workflow against experimental data for various ions.
• To enable theoretical predictions for ions lacking experimental data, such as radioactive species.

Main Methods:

• Developed the ISAIAH (Ion Simulation using AMBER for dIffusion Action when Hydrated) workflow.
• Simulated diffusion coefficients for 15 monoatomic ions (charges -1 to +3) using four water models.
• Evaluated force field parameter sets, focusing on augmented 12-6-4 Lennard-Jones (LJ) potentials versus standard 12-6 LJ potentials.

Main Results:

• The ISAIAH workflow demonstrated good agreement with experimental diffusion coefficient values.
• Augmented 12-6-4 LJ potentials showed lower average unsigned errors (AUE) compared to 12-6 LJ parameters for various ions.
• The 12-6-4 model effectively captures factors influencing diffusion, such as hydration free energy (HFE) and ion-oxygen distance (IOD).

Conclusions:

• The ISAIAH workflow provides a reliable method for simulating ion diffusion coefficients.
• The augmented 12-6-4 LJ potential is superior for accurately modeling ion diffusion in water.
• This work enables theoretical predictions for challenging ions, including 239Pu4+, advancing safety and research in hazardous material handling.