Development of Multiscale Force Field for Actinide (An³⁺) Solutions

A multiscale force field (FF) is developed for an aqueous solution of trivalent actinide cations An³⁺ (An = U, Np, Pu, Am, Cm, Bk, and Cf) by using a 12-6-4 Lennard-Jones type potential considering ion-induced dipole interaction. Potential parameters are rigorously and automatically optimized by the meta-multilinear interpolation parametrization (meta-MIP) algorithm via matching the experimental properties, including ion-oxygen distance (IOD) and coordination number (CN) in the first solvation shell and hydration free energy (HFE). The water solvent models incorporate an especially developed polar coarse-grained (CG) water scheme named PW32 and three widely used all-atom (AA) level SPC/E, TIP3P, and TIP4P water schemes. Each PW32 is modeled as two bonded beads to represent three neighboring water molecules, the simulation efficiency of which is 1 to 2 orders of magnitude higher than that of AA waters. The newly developed FF shows high accuracy and transferability in reproducing the IOD, CN, and HFE of An³⁺. The molecular structure and water exchange dynamics of the first An³⁺ hydration shell and the ionic (van der Waals) radii are reinvestigated in this work. Moreover, the new FF can readily be transferred to other popular FFs, as it has practicably predicted the permeability of An³⁺ in a graphene oxide filter within the framework of optimized potentials for liquid simulations (OPLS)-AA FF. It holds promise for applications in exploring actinide aqueous solutions with multiscale computational overhead.