Polarizable molecular interactions in condensed phase and their equivalent nonpolarizable models

TL;DR

This paper investigates how polarizable molecular models in condensed phases can be simplified to nonpolarizable models with scaled charges, providing theoretical insights into the origin and conditions of such reductions.

Contribution

It offers a theoretical framework explaining the derivation of nonpolarizable models from polarizable ones and clarifies the conditions under which this reduction is valid.

Findings

Scaling factors are derived from electronic polarization screening effects.

Theoretical models explain the origin of charge scaling in simplified models.

Conditions for valid reduction from polarizable to nonpolarizable models are identified.

Abstract

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.