For the final solute-solvent system, we chose the [Fe(bpy) 3 ] 2+ (bpy = 2,2'-bipyridine) complex in water, as it has been central to many previous x-ray solution scattering experiments and theoretical studies of solute-solvent interactions . The complex was parameterized within the General AMBER (GAFF) potential, using the 'MCPB.py' method, as described elsewhere . The complex was then solvated in a box of 7329 water molecules modelled with the TIP4P EW potential , using the 'leap' program from the 'Ambertools' toolbox . Two Cl -counterions were also added using leap, to charge-neutralize the system. The complex was restrained in the center of the box, and the counterions were restrained roughly 22 Å away from the complex using positional restraints with 500 kcal/mol force constants. The NPT equilibration resulted in a final cell size of (58.7 x 61.1 x 61.4) Å. The density and temperature were equilibrated using OpenMM for 500 ps in the NPT ensemble, using a Monte Carlo Thermostat to keep the pressure at 1 bar, and a Langevin propagator to keep the temperature at 300 K . As with the previous set of simulations the simulation cell size was changed to sample each global density in the NVT ensemble for 20 ns.