We set up simulation systems consisting of two opposing monolayers, separated by a water slab on the hydrophilic side and the gas phase on the hydrophobic side, as shown in Figure of the Supporting Information (SI). This set up leads to periodically symmetric interfaces, when periodic boundary conditions are applied. Our main simulation systems, denoted as S400, are composed of smaller monolayers with 400 lipids, while we also simulate additional, larger systems that feature monolayers of 3200 lipids, denoted as L3200. Several S400 systems as constructed at different lateral sizes (𝑥 and 𝑦 ), corresponding to area per lipid, 𝑎 𝐿 ranging from 0.51 𝑛𝑚 2 to 1.54 𝑛𝑚 2 , keeping the number of particles in the system constant; the number of water beads, 𝑁 𝑊 and gas beads 𝑁 𝐺 are 52720, while the total number of particles, 𝑁 𝑡𝑜𝑡 = 116640. This means that, as the lateral size is increased to higher 𝑎 𝐿 , the normal size 𝑧 of the system is reduced accordingly, so that the system volume remains constant. Thus, the S400 normal size varies from 𝑧 = 26.23 𝑅 𝑐 (17.0 nm) at 𝑎 𝐿 = 1.54 𝑛𝑚 2 to 𝑧 = 78.4 𝑅 𝑐 (50.7 𝑛𝑚) at 𝑎 𝐿 = 0.51 𝑛𝑚 2 , while the lateral size varies from 𝑥, 𝑦 = 38.38 𝑅 𝑐 (24 nm) to 𝑥, 𝑦 = 22.1 𝑅 𝑐 (14.3 𝑛𝑚). In the L3200 systems, the total number of particles are 𝑁 𝑡𝑜𝑡 = 574200 with 𝑁 𝑊 = 𝑁 𝐺 = 242300 and the system dimensions vary from 56.4 × 56.4 × 16.1 𝑛𝑚 3 to 41.8 × 41.8 × 29.2 𝑛𝑚 3 as 𝑎 𝐿 varies from 0.99 𝑛𝑚 2 to 0.49 𝑛𝑚 2 .