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Dynamic Implicit-Solvent Coarse-Grained Models of Lipid Bilayer Membranes : Fluctuating Hydrodynamics Thermostat 

In this project we use the Stochastic Eulerian Lagrangian Method (SELM), with the natural Lagrangian reference frame to represent the coarse-grained lipids and the Eulerian reference frame to represent the fluid. We use this SELM method to include more accurate hydrodynamics into a three-bead coarse-grained lipid bilayer model, see Ira Cooke, Kurt Kremer, and Markus Deserno (2005). We have promising results that show significant differences in behavior, when the hydrodynamics are accounted for, both in the case of a periodic bilayer sheet and in the case of a vesicle.
The core challenges in this work are to further develop the coarse-grained model to access larger length and time-scales for more complex biophysical systems. Also, there are some intrinsic numerical challenges to making the methods computationally more efficient. Furthermore, there is the importance of good coupling operators that couple the structures to the fluid and exhibit good translation invariance properties for the structures.

Soft matter physics, and in particular the lipid bilayer membrane, is a setting of length and time-scales where thermal fluctuations play a significant role. Hence, the importance of a framework that incorporates thermal fluctuations and hydrodynamics in a way that is consistent with statistical mechanics. 

We are currently in the process of looking at quantitative differences after having incorporated those more accurate hydrodynamics. We have shown how this approach captures correlations in the dynamics of lipid bilayers that are missing in simulations performed using conventional Langevin dynamics. For both periodic sheets and vesicles, we investigate the diffusivity of lipids, spatial correlations, and lipid flow within the bilayer. This work is being carried out in collaboration with Yaohong Wang, Erik Brandt and Paul J. Atzberger. 

Paper

Dynamic implicit-solvent coarse-grained models of lipid bilayer membranes : Fluctuating hydrodynamics thermostat, Yaohong Wang, Jon K. Sigurdsson, Erik Brandt, and Paul J. Atzberger, Physical Review E, 88 (2013), pp. 023301–.
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