Group Polarizability Model for Molecular Mechanics Energy Functions

A polarization model for molecular mechanics energy functions is developed that is based on a local group paradigm, namely the polarizability of a rigid substructure of covalently connected atoms. Axes at a "diffuse" site within the group define an anisotropic local group polarizability as well as hyperpolarizability. The theoretical basis for this model is presented, and its performance is described through applications to water, alkanes, and N-methylacetamide. The excellent agreement with quantum mechanical electric potentials and molecular polarizabilities indicates that this model must be considered an important candidate for the inclusion of polarization into such force fields. The ab initio-based spectroscopically determined force field (SDFF) protocol for the calculation of parameters assures that, in addition to structures and energies, forces will be accurately modeled.