  We present a simple and computationally efficient coarse-grained and
solvent-free model for simulating lipid bilayer membranes. In order to be used
in concert with particle-based reaction-diffusion simulations, the model is
purely based on interacting and reacting particles, each representing a coarse
patch of a lipid monolayer. Particle interactions include nearest-neighbor
bond-stretching and angle-bending, and are parameterized so as to reproduce the
local membrane mechanics given by the Helfrich energy density over a range of
relevant curvatures. In-plane fluidity is implemented with Monte Carlo
bond-flipping moves. The physical accuracy of the model is verified by five
tests: (i) Power spectrum analysis of equilibrium thermal undulations is used
to verify that the particle-based representation correctly captures the
dynamics predicted by the continuum model of fluid membranes. (ii) It is
verified that the input bending stiffness, against which the potential
parameters are optimized, is accurately recovered. (iii) Isothermal area
compressibility modulus of the membrane is calculated and is shown to be
tunable to reproduce available values for different lipid bilayers, independent
of the bending rigidity. (iv) Simulation of two-dimensional shear flow under a
gravity force is employed to measure the effective in-plane viscosity of the
membrane model, and show the possibility of modeling membranes with specified
viscosities. (v) Interaction of the bilayer membrane with a spherical
nanoparticle is modeled as a test case for large membrane deformations and
budding involved in cellular processes such as endocytosis...
