As a result of the asymmetrical stress within the lipid bilayer induced by the Ca 2+ ions, the membrane tends to bend to release the stress. This tendency for the membrane to bend can be characterized by the spontaneous curvature c 0 in the classical Helfrich model, which has been widely used to model the deformation of a membrane on a large scale. Herein, we studied the deformation of a spherical vesicle with a diameter of 100 nm with the Helfrich model, by employing the MD simulation results as the input physical parameters. Basically, we estimated the spontaneous curvature induced by the asymmetrically distributed Ca 2+ ions via Eq. ( ) based on the integral of the irst moment of LPPs obtained from MD simulation analyses, which were then input to the Helfrich model to calculate the steady shape of the vesicle (see Continuum Mechanics Calculation in the section of Materials and Methods for a detailed description).