Regensburg 2010 – scientific programme

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BP: Fachverband Biologische Physik

BP 19: Membranes and Vesicles

BP 19.4: Talk

Wednesday, March 24, 2010, 10:45–11:00, H43

Free energy calculations of the main phase transition in lipid bilayers — •Martin Hömberg and Marcus Müller — Institut für Theoretische Physik, Georg-August-Universität Göttingen, 37077 Göttingen, Germany

In coarse-grained models of lipid bilayers one integrates out local degrees of freedom, so that the study of collective phenomena, like phase transitions, lateral phase separation in heterogeneous bilayers, and self-assembly, becomes feasible in computer simulations. However, the precise calculation of phase diagrams is still a formidable task due to hysteresis effects and metastability in the vicinity of phase transitions.

Here we employ DPD for the simulation of a coarse-grained solvent-free model for single component lipid bilayers. The non-bonded interactions between the lipids are derived from an excess free energy, which takes the form of a weighted density functional. We find a rich phase diagram, study the main phase (liquid-gel) transition, and present a method to calculate the free energy at this transition as a function of an orientational order parameter. We apply a combination of Umbrella Sampling and histogram reweighting techniques for transforming the liquid phase reversibly into a gel phase. We are able to locate the phase transition point precisely from the free energy profile and we obtain a value of the line tension between liquid and gel domains. This value is compared to the value obtained from a spectral analysis of the boundary fluctuations of gel domains in a liquid phase.