To compare the OPLS3e and CHARMM36 force fields to experimental data we performed equally long MD simulations (lengths ranging from 500 ns to 1μs) using both force fields with matching hydration levels (Table ) and salt concentrations (Table ). Here we note just the key simulation details; all details are available in the run input files of the corresponding trajectories on Zenodo, see Tables and for the permanent links. Simulations used standard setup for planar bilayers, zero tension and periodic boundary conditions in either Desmond, implemented in Schrödinger suite package version 2019.4 (33, 34) (OPLS3e), or in GROMACS version 2019.5 (CHARMM36). All simulated systems contained 200 POPC lipids (100 per leaflet) and they were generated using the system builder and the model system regeneration tools of the Schrödinger software suite and CHARMM-GUI Membrane builder, respectively. The NPT ensemble with temperature of 300 K and 1 atm pressure was used. In the simulations containing ions, ions were initially placed randomly in the water phase. Only the steady-state part of the simulations was analyzed, that is, after the bilayer area per lipid stabilized and (in salt-containing systems) no further ions accumulated in the membrane. Notably, the OPLS3e with high CaCl 2 concentration did not reach a steady state during 1μs, so the simulation was divided into 10x100 ns parts analyzed separately. Details of the simulations with varying hydration levels are shown in Table , and with varying concentrations of additional salt in Table