Energy barriers for dissociation are approximated by ∆G between the first energy maximum and the first energy minimum in the FES, whereas relative stabilities of different metastable states are determined as free energy differences between them as shown in Figure (right). It is to be noted that since the MD simulations are performed in the N V T ensemble, the free energies obtained with the biased simulations are the Helmholtz free energies. However, as shown in Schulze et al. , the change in volume due to the addition of an associated ion pair or a dissociated ion pair is negligibly small at solvent density of ∼0.8 g/cm 3 . These effects can therefore be neglected and the Helmholtz free energies can be considered to be approximately equal to the Gibbs free energies.