To quantify the effect of hydration on the binding, we simulated systems with a fixed etidocaine concentration in simulation boxes with the z-dimension ranging from 5 nm to 81 nm. The lower limit corresponds to a typical size for membrane simulations, and the upper limit corresponds to the water-lipid ratio used in the experimental setup for etidocaine. For parameters predicting the weakest binding affinity, CHARMM36-SwissParam, the results are similar with box sizes above approximately 12 nm in the z-direction (Figs. S4 and S5 in the SI). However, in simulations with CHARMM36-ParamChem and CHARMM36-ParamChem-ECC predicting stronger binding affinities, the dependence on the box size is observed also above z-dimensions of 12 nm. Further simulations with these parameters were, therefore, run using the large box with the z-dimension of approximately 81 nm, while boxes with the zdimension of approximately 12 nm were used for other systems with weaker binding affinities to reduce the computational cost. Because binding of charged molecules to zwitterionic PC membranes substantially increases the lamellar repeat distance in a lipid bilayer stack, we consider such a large interbilayer space reasonable for the studies of strongly membranebound charged molecules.