Atomistic MD simulations of membrane systems have been previously used to research the effects of changing different physiologically relevant conditions, such as the hydration level, and the ion concentrations . Lower hydration is relevant in studying many biological processes, such as membrane fusion ; ions are present in all biological systems, and ion-membrane interactions are of a key importance e.g., in neuron studies . Experimental studies have shown that the phosphatidyl choline headgroup order parameters rise in response to lowering hydration and drop in response to cation binding . A good quality atomistic level force field should also capture these changes.