MOLECULAR-DYNAMICS SIMULATIONS OF A FULLY HYDRATED DIPALMITOYL PHOSPHATIDYLCHOLINE BILAYER WITH DIFFERENT MACROSCOPIC BOUNDARY-CONDITIONS AND PARAMETERS

We compared molecular dynamics simulations of a bilayer of 128 fully h ydrated phospholipid (DPPC) molecules, using different parameters and macroscopic boundary conditions. The same system was studied under con stant pressure, constant volume, and constant surface tension boundary conditions, with two different sets of charges, the single point char ge (SPC) and extended single point charge (SPC/E) water model and two different sets of Lennard-Jones parameters for the interaction between water and methyl/methylene. Some selected properties of the resulting bilayer systems are compared to each other, previous simulations, and experimental data. It is concluded that in relatively high water conc entration it is possible to use ab initio derived charges with constan t pressure boundary conditions. The SPC water model gives a larger are a per head group and a broader interface than the SPC/E model. Increas ing the repulsion between water oxygens and CH2/CH3 groups has a large effect on the width of the interface and the area per head group. The re is little difference between simulations with constant pressure and constant surface tension. The use of constant volume, using a reasona ble estimate for the initial box dimensions, easily introduces artefac ts. (C) 1996 American Institute of Physics.