Analyzing Many-Body Charge Transfer Effects With the Fragment Molecular Orbital Method.

A many-body expansion of charge transfer (CT) energies is developed for the fragment molecular orbital method. It is applied to decouple CT and mix terms in interaction energy decomposition analyses. Many-body charge transfer is graphically illustrated in the form of frontier orbital diagrams. The contribution of CT to molecular interactions is elucidated in the application of the method to water clusters, solvated ions, and polypeptide motifs.