CH affinity and equilibration is consequently faster (Fig. ). S α CH and S β CH also show decline as a function of simulation time in OPLS3e as the number of ions in vicinity of the membrane keeps rising, see Fig. but not in CHARMM36 (Fig. ). Over binding of ions to membranes is a problem in most of the current force fields and based on our studies this is the case also with OPLS3e force field. One reason behind the over binding might be too high charge of the ions. In previous studies, it has been proposed that scaling the ion charge might help to overcome mistakes resulting from the lacking electronic polarization . In electronic continuum correlation (ECC) theory, based on quantum mechanical calculations, scaling factor of ions is 0.75. This scaling of ion charges has been able to improve monovalent ion binding in some force fields, but has not been sufficient for the divalent CaCl 2.