  Earlier, using phenomenological approach, we showed that in some cases
polarizable models of condensed phase systems can be reduced to nonpolarizable
equivalent models with scaled charges. Examples of such systems include ionic
liquids, TIPnP-type models of water, protein force fields, and others, where
interactions and dynamics of inherently polarizable species can be accurately
described by nonpolarizable models. To describe electrostatic interactions, the
effective charges of simple ionic liquids are obtained by scaling the actual
charges of ions by a factor of 1/sqrt(eps_el), which is due to electronic
polarization screening effect; the scaling factor of neutral species is more
complicated. Here, using several theoretical models, we examine how exactly the
scaling factors appear in theory, and how, and under what conditions,
polarizable Hamiltonians are reduced to nonpolarizable ones. These models allow
one to trace the origin of the scaling factors, determine their values, and
obtain important insights on the nature of polarizable interactions in
condensed matter systems.
