Development of\nMultiscale Force Field for Actinide\n(An<sup>3+</sup>) Solutions

A multiscale force field (FF) is developed for an aqueous\nsolution\nof trivalent actinide cations An<sup>3+</sup> (An = U, Np, Pu, Am,\nCm, Bk, and Cf) by using a 12-6-4 Lennard-Jones type potential considering\nion-induced dipole interaction. Potential parameters are rigorously\nand automatically optimized by the meta-multilinear interpolation\nparametrization (meta-MIP) algorithm via matching the experimental\nproperties, including ion-oxygen distance (IOD) and coordination number\n(CN) in the first solvation shell and hydration free energy (HFE).\nThe water solvent models incorporate an especially developed polar\ncoarse-grained (CG) water scheme named PW32 and three widely used\nall-atom (AA) level SPC/E, TIP3P, and TIP4P water schemes. Each PW32\nis modeled as two bonded beads to represent three neighboring water\nmolecules, the simulation efficiency of which is 1 to 2 orders of\nmagnitude higher than that of AA waters. The newly developed FF shows\nhigh accuracy and transferability in reproducing the IOD, CN, and\nHFE of An<sup>3+</sup>. The molecular structure and water exchange\ndynamics of the first An<sup>3+</sup> hydration shell and the ionic\n(van der Waals) radii are reinvestigated in this work. Moreover, the\nnew FF can readily be transferred to other popular FFs, as it has\npracticably predicted the permeability of An<sup>3+</sup> in a graphene\noxide filter within the framework of optimized potentials for liquid\nsimulations (OPLS)-AA FF. It holds promise for applications in exploring\nactinide aqueous solutions with multiscale computational overhead.