For more detailed comparison of membrane structure, we interpolated the changes in electron density proles along membrane normal (Fig. ) as a function of CHOL concentration to create two-dimensional electron density maps (Fig. ). Overall, all electron density proles share the same features across all CHOL concentrations: High densities corresponding to the tightly-packed interfacial regions containing the electron-rich phosphorus, low density at the core of the membrane occupied by the disordered acyl chains, and intermediate density in the rest of the lipid regions as well as the aqueous phase. However, a more detailed look at the proles in Fig. reveals dierences between the force elds and the SPD model.