Free energy landscapes of ion coordination issuing from MD simulations of Na+ in aqueous solution with normal sampling. The plot shows the results obtained using fixed charges with GROMOS96 parameters (black, Na1), fluctuating charges with GROMOS96 parameters (red, Na2), fluctuating charges modifying only σ (blue, Na3) and fluctuating charges modifying both σ and ε (green, Na4). Panel B: comparison of standard and modified Lennard-Jones potential energies used in Na+ simulations, using the same color convention as above.