  Implicit solvent, coarse-grained models with pairwise interactions can access
the largest length and time scales in molecular dynamics simulations, owing to
the absence of interactions with a huge number of solvent particles, the
smaller number of interaction sites in the model molecules, and the lack of
fast sub-molecular degrees of freedom. In this paper, we describe a maximally
coarse-grained model for lipids in implicit water. The model is called
SiMPLISTIC, which abbreviates for Single-site Model with Pairwise interaction
for Lipids in Implicit Solvent with Tuneable Intrinsic Curvature. SiMPLISTIC
lipids rapidly self-assemble into realistic non-lamellar and lamellar phases
such as inverted micelles and bilayers, the spontaneous curvature of the phase
being determined by a single free parameter of the model. Model membrane
simulations with the lamellar lipids show satisfactory fluid and gel phases
with no interdigitation or tilt. The model lipids follow rigid body dynamics
suggested by empirical studies, and generate bilayer elastic properties
consistent with experiments and other simulations. SiMPLISTIC can also simulate
mixtures of lipids that differ in their packing parameter or length, the latter
leading to the phenomenon of hydrophobic mismatch driven domain formation. The
model has a large scope due to its speed, conceptual and computational
simplicity, and versatility. Applications may range from large-scale
simulations for academic and industrial research on various lipid-based
systems, such as lyotropic liquid crystals, biological and biomimetic
membranes, vectors for drug and gene delivery, to fast, lightweight,
interactive simulations for gaining insights into self-assembly, lipid
polymorphism, biomembrane organization etc.
