The overall free energy between the oligomers and the Li + ion was determined without following any specific pathways. We instead performed an extensive sampling of the systems to obtain well-converged radial density profiles (RDPs), ρ ij (r), between the center of mass (COM) of oligomer i and ion j as a function of their distance r. To have a well-defined reference value of the free energy, the RDPs were normalized by the bulk density, ρ 0 , defining the dimensionless distribution function g ij (r) = ρ ij (r)/ρ 0 . The bulk density was estimated from the density profile near the boundaries of the simulation box, where the profile converges and significant fluctuations are absent. The free energy, ∆F ij (r), as a function of distance, also called the potential of mean force (PMF) along the radial direction, was then obtained using a standard Boltzmann inversion: