Bead sizes. To parametrize DPPC bead types, we adopt the approach recently developed by Anderson et al, with some modifications. The bead diameter, 𝑅 𝐼𝐼 , of the bead types are calculated based on the partial molar volumes, 𝑉 𝐼 , obtained using the method of Durchslag and Zipper (DZ), 𝑅 𝐼𝐼 3 ∝ 𝑉 𝐼 . DZ method determines the partial molar volume of a group of atoms by summing the increments from each atom, a co-volume, and contributions due to charge and ring formation. 𝑅 𝐼𝐼 is also the intra-bead interaction cutoff for the DPD forces. The inter-bead cutoffs 𝑅 𝐼𝐽 are calculated by adopting the mixing rule 𝑅 𝐼𝐽 = 1 2 (𝑅 𝐼 + 𝑅 𝐽 ). The approach of Anderson et al allows variable bead sizes, improving on the equal bead volume approach of Groot and Warren. For the DPPC head group, the N and P beads are of different sizes. The glycerol backbone must be represented by two beads of different sizes, as no division can result in two beads of identical type. Similarly, due to the presence of CH3 group, the end bead E must be of different size than the C bead. Here, we deviate from the scheme of Anderson et al, and represent the glycerol backbone as two identical beads and the lipid tails as five beads of equal size. This approach is adopted for two key reasons: (1) For amphiphilic molecules such as DPPC, which form bilayer and monolayer phases, lipid packing is crucial. The area per lipid, denoted as 𝑎 𝐿 , is a critical parameter for phospholipid films, influencing their mechanical and phase behaviors. Therefore, it is essential that both the glycerol backbone and tails to have the correct volume and packing. Especially, at low 𝑎 𝐿 values, these beads are tightly packed, unlike N and P beads which enjoy more space due to the lipid being double-tailed. (2) Different bead sizes may result in local density variations, which are unsuitable for describing the 2D monolayer/bilayer phases formed by DPPC, including gel/liquid crystalline, and liquid expanded/liquid condensed phases, which have uniform density. The partial molar volume of the G bead is obtained by halving the volume of glyceryl diacetate after subtracting the volume of an OH group and two CH3 groups (see Supporting Information). The volume of the C/E beads is calculated as one fifth of the volume of pentadecane excluding a hydrogen atom. Note that the C and E beads are identical; they are labeled differently only for convenience of analyzing the data. The calculated bead sizes relative to the water bead (units of 𝑅 𝑐 ) are provided in