Both MMG-1 and MMG-6 were simulated in three different membrane configurations: 1) a non-interdigitated single bilayer, 2) a non-interdigitated double bilayer, and 3) a fully interdigitated double bilayer (Table ). These configurations were chosen based on the X-ray scattering study by Martin-Bertelsen et al., which showed that MMG analogs selfassemble into poorly hydrated lamellar structures at low temperatures. We used double bilayer configurations to represent these structures, because they have been shown to contain little or no water. 11 The single bilayer configuration was included to allow comparison of different hydration states. All systems contained one of the two analogs as a 1:1 mixture of two stereoisomers. System sizes were selected to allow for an accurate representation of possible interdigitation or membrane rippling in the non-interdigitated membranes. Finite size effects are known to quench certain membrane phenomena, e.g., ripple phase formation and membrane undulations. Moreover, system size has been shown to affect the extent of stretch-induced interdigitation with united atom MD simulations. Therefore, the non-interdigitated membranes were configured to contain 256 MMG molecules per leaflet. The interdigitated system was built with 64 MMG molecules per leaflet. Since the interdigitated system was observed to be fully planar without defects or undulations, the small system size was, in this case, deemed adequate. Preliminary simulations of non-interdigitated double bilayers were also conducted with small systems, which contained 64 MMG molecules per leaflet. The results from these simulations are presented in Figures S1.1-S1.14, and Tables S1.1-S1.4. The results show similar trends as the larger double bilayer system, but the differences between the two MMG analogs are less pronounced due to reduced sampling. The small double bilayer structures obtained after the first equilibration step were used to build the large double bilayer structures.