Non-ideal mixing of lipids: a molecular dynamics perspective

Lipid membranes have complex compositions and modeling the thermodynamic properties of multi-component lipid systems remains a remote goal. In this work we attempt to describe the thermodynamics of binary lipid mixtures by mapping coarse-grained molecular dynamics systems to two-dimensional simple fluid mixtures. By computing and analysing the density fluctuations of this model lipid bilayer we determine the numerical value of the quadratic coupling term appearing in a model of regular solutions for the DPPC-DLiPC pair of lipids at three different compositions. Our methodology is general and discussed in detail.