Polarizable Mean-Field Model of Water for Biological Simulations with AMBER and CHARMM Force Fields

Although a great number of computational models of water are available today, the majority of current biological simulations are done with simple models, such as TIP3P and SPC, developed almost 30 years ago and only slightly modified since then. The reason is that the nonpolarizable force fields that are mostly used to describe proteins and other biological molecules are incompatible with more sophisticated modern polarizable models of water. The issue is electronic polarizability: in a liquid state, in protein, and in a vacuum, the water molecule is polarized differently and therefore has different properties; thus the only way to describe all of these different media with the same model is to use a polarizable water model. However, to be compatible with the force field of the rest of the system, e.g., a protein, the latter should be polarizable as well. Here, we describe a novel model of water that is in effect polarizable and yet compatible with the standard nonpolarizable force fields such as AMBER, CHARMM, GROMOS, OPLS, etc. Thus, the model resolves the outstanding problem of incompatibility.