Constant surface tension simulations of lipid bilayers: The sensitivity ofsurface areas and compressibilities

Eight molecular dynamics simulations of a hydrated lipid bilayer have been carried out differing only in the applied surface tension, gamma, defining the boundary conditions of the periodic cell. The calculated surface area p er molecule and deuterium order parameter profile are found to depend stron gly on gamma. We present several methods to calculate the area compressibil ity modulus, K-A, from the simulations. Equivalence between the constant ar ea and constant surface tension ensembles is investigated by comparing the present simulations with earlier work from our laboratories and we find sim ulation results to depend much more strongly on the specified surface area or surface tension than on the ensemble employed. (C) 1999 American Institu te of Physics. [S0021-9606(99)71327-9].