The functional form of the second-generation force fields is described the Supporting Information. The atomic types of the ligand molecule were assigned to follow the original COMPASS force field. The parameters for the flexible model of water were taken from the PCFF. The assigned atomic types (c3a and h1) in DBM were labeled using the original COMPASS force-field database, as shown in Fig. . Some of the atoms in the ligand, along with Ho, were missing from the database, and these are shown in red in Fig. . The intermolecular (bond, angle, dihedral, and improper) and/or vdW parameters of o1=, c3', c3b, hb, and Ho were thus newly parameterized in this study. It is noted that the COMPASS force field uses a Lennard-Jones (LJ) 9-6 functional form for the vdW interaction instead of an LJ 12-6 functional form. The sixth-order combination law 41 was applied to the LJ 9-6 parameters for the assigned atomic types. The partial charges of Ho and its neighboring atoms for the Coulomb interaction were determined by considering charge transfer. The partial charge of Ho, q Ho , was compensated with the surrounding atoms, thus the charge transfer was addressed to six (o1=)s in DBM: