A refined polarizable water model for the coarse-grained MARTINI force field with long-range electrostatic interactions

We present a refined version of the polarizable MARTINI water model - coined refPOL - designed specifically for the use with long-range electrostatics. The refPOL model improves the agreement with the experimentally measured dielectric constant and the mass density of water at room temperature compared to the original polarizable MARTINI water force field when particle mesh Ewald electrostatics are employed. Our study reveals that the model remains applicable with various commonly used settings for the non-bonded interactions, including reaction field electrostatics. The oil/water partitioning behavior of uncharged MARTINI bead types is thoroughly investigated: Lennard-Jones interactions between the refPOL model and the remaining MARTINI beads are adjusted to reproduce the hydration free energies obtained with the original polarizable water model, while free energies of solvation in apolar media remain unchanged. The cross-interactions with charged bead types are parameterized to agree with the experimentally observed area per lipid of a fully solvated dipalmitoylphosphatidyl-choline bilayer. We additionally verify the model by analyzing the potentials of mean force between different sample pairs in refPOL water and comparing the results to reference data obtained using the original polarizable MARTINI water model as well as fully atomistic simulations. Based on the results, we suggest to replace the original polarizable MARTINI water model with the new refPOL model for future applications. Published by AIP Publishing.