Fig 3. (a) Perturbed Helmholtz free-energy change (useful work) of three-ion pulling configurations. The value of λ indicates the center of the harmonic pulling potential (see Fig 1). (b) Perturbed Helmholtz free-energy change (useful work) of individual ions in the three-ion pulling simulations. The numbers indicate the ordered ions in the three-ion configurations. (c) Averaged z-coordinate of three ions.