Many protein RNA-complexes contain bound ions which we also had in all our systems. Ions as charged particles pose a challenge for the non-polarizable force fields which could be observed as the ions unbinding. The issues of ions in nonpolarizable force fields have been described many times before (for example , and there are no easy solutions. Seeing that the ions sometimes unbind also in the polarizable force fields, the only feasible solution is to constrain the structurally important ions positionally unless one especially wants to study the ion unbinding.