Hybrid quantum mechanical molecular mechanical fluctuating charge models for condensed phase simulations

Hybrid quantum mechanical/molecular mechanical potentials have proved to be powerful tools for the simulation of many processes in condensed phase systems and, as a result, there is much current research into how they can be improved. An area of recent attention has been the inclusion of polarization effects on the atoms in the molecular mechanical region which have been shown to be important for the calculation of certain properties. One way to treat such effects is with a dipole polarizability model. However, an alternative and, in many ways, simpler method is available that is based upon the principle of electronegativity equalization. In this paper a number of hybrid potentials are presented that employ a fluctuating charge model and electronegativity equalization to describe the electrostatic interactions in the molecular mechanical region of the system. The models are straightforward to implement and their use is illustrated with applications to some simple solution phase systems.