Tom Keyes

Enhanced sampling of phase transitions in water, lipids, and lipid-wrapped nanoparticles

Computer simulation of phase transitions is challenging when using temperature as the control parameter because surface effects raise the free energy of the states with coexisting phases and create a barrier which makes the equilibrium pathway difficult to access. We have developed two algorithms, the generalized replica exchange method (gREM) and statistical temperature molecular dynamics (STMD), to deal with those difficulties. The algorithms and the associated entropic approach to phase transitions will be described and applied to water, lipid bilayers and vesicles. For a lipid bilayer wrapped around a spherical core, a hybrid MD/MC algorithm which lets the core adjust for a given number of lipids will be presented and used to obtain the numbers in the inner and outer layers, and their gel/fluid transition, vs core radius.