An application of improved force field to fully hydrated DPPC and POPC bilayers in a tensionless NPT ensemble: a test of CHARMM 27-based new force field by Högberg et al.

Recently developed all-atom potential model by Hogberg et al. has been applied to 1,2-di-palmitoyl-phosphatidylcholine (DPPC) and 1-palmitoryl-2-oleoyl-phosphatidylcholine (POPC) fully hydrated lipid bilayers. Tensionless NPT ensemble calculations have been performed over 40 ns to test the performance of the force field at 1 atm and at 323.15 and 303.15 K, respectively, where we focused our attention on the membrane area and the order parameter. The calculated membrane area per lipid molecule was 0.669 and 0.653 nm2 for DPPC and POPC, respectively, which shows a good agreement with the experimental values 0.642 and 0.683 nm2, respectively. This is an extensive improvement over the original CHARMM 27 or CHARMM 27r, which gives gel-like very small value of the membrane area 0.49 and 0.574 nm2, respectively. Furthermore, the calculated order parameter of C–H vector in acyl tails and electron density profile also show good correspondence with the experiment.