Molecular Mechanics with QEq-CS: Charge Equilibration Method Generalized for Charge Separation System

In this article we put forward an idea to find a crossing point of a photoinduced electron transfer reaction of a large system such as a photosynthetic reaction center. The system requires describing the energy by Molecular Mechanics (MM) with the charge equilibration method generalized for a charge separation system (QEq-CS). The QEq-CS determines atomic charges on system circumstances, and reproduces ab initio results. A combination of MM with QEq-CS and Koga-Morokuma scheme shows the useful applications to two test cases consisting of three benzene molecules.