There are still some details that are dependent on the ion model and parameters adopted in the MD simulations. With the new multisite ion model, Ca 2+ ions were found to be stably bound to the anionic groups of lipid molecules, with similar afinity to the phosphate groups and carboxylate groups (Table ). This is different from the previous simulation results that revealed a strong binding preference of Ca 2+ to carboxylate groups, as also observed in our simulations with the default Ca 2+ model. Notably, previous infrared absorption spectroscopy experiments suggested that Ca 2+ ions probably do not stably bind to the carboxylate groups in PS, but can bind to phosphate groups to induce dehydration. There were also experiments showing that Ca 2+ can bind to both carboxylate and phosphate groups of PS. In this aspect, our new multisite Ca 2+ model may have the advantage of reducing the binding bias to carboxylate groups. Nonetheless, although these local differences resulting from speciic ion models are appreciable, they do not generate qualitative differences in the global properties of the bilayers discussed in this work.