where n h is the hydration shell size where the solvated ion complexes start to repel each other and N A is Avogadro's constant. In general, n h will be different for different orders of the multipole expansion. Heuristically, we found that electrolyte activities can be well represented when allowing n Dipole h ≥ 0 (this corresponds to x Dipole h ≤ 1) while keeping n h = 0 (i.e. x h = 1) for the quadrupole and octupole contributions. The average apparent molar volume in the solution is given by ϕ sol = M sol /ρ sol where M sol = xM B + (1 -x)M w and ρ sol are the average molar mass and the density of the solution, respectively.