Figure 4.

Average density profile of different species as a function of the z coordinate (perpendicular to the membrane) obtained from MD simulations. Solid line: water density (molecules/nm³); dashed line: oxygen atoms of O2 type from lipid molecules (atoms/nm³); dotted line: number density of divalent cations (ions/nm³) multiplied by a factor of 10 for clarity. Shown are simulations with (a) Ca²⁺ and (b) Mg²⁺. (Inset) Snapshot from MD simulations. Hydrocarbon tails are shown schematically as lines and divalent cations, oxygen atoms of O2 type from lipids and hydration water molecules are highlighted. To aid in interpretation of the figure, we also show schematically the hydrocarbon tails as lines.