Ammm:Mm aplus

Introduction

One is recommended to read through and understand the background knowledge of polarizable force field AMOEBA, in order to have a better learning experience of the next generation AMOEBA+ force field. As indicated by the name, AMOEBA+ is based on the AMOEBA framework with incoporation of essential physical effects that are missing in AMOEBA model. With the short-range charge penetration and charge transfer effects being included, AMOEBA+ potential is able to follow the energy components by the Symmetry Adapted Perturbation Theory (SAPT).

Below brief description of the SAPT theory is introduced, followed by the specific interactions/physical effects that are incoporated in AMOEBA+ potential. In the last part, brief summary of the current status of the parametrization of the AMOEBA+ force field is given.

SAPT Method

Intermolecular interactions are small (comparing to the intramolecular interactions). For example, helium dimers at equalibrium only has interaction atoms of -0.02 kcal/mol. However, the intermolecular interactions are important for describing a lot of phenomina in chemistry, physics and biology.

Starting from a dimer AB composed of two monomers, A and B, the interaction energy is computed as:

$E_{int}=E_{AB}-E_{A}-E_{B}$

This is often called super molecule approach to calculate intermolecuar energies.

New Potential Energy Terms

These energy terms are newly added, which means they are not in the AMOEBA model.