  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 thirty years ago and only slightly
modified since then. The reason is that the non-polarizable 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 liquid state, in protein, and in vacuum
the water molecule is polarized differently, and therefore has different
properties; thus the only way to describe all 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 non-polarizable force fields
such as AMBER, CHARMM, GROMOS, OPLS, etc. Thus the model resolves the
outstanding problem of incompatibility.
