Redistributed charge and dipole schemes for combined quantum mechanical and molecular mechanical calculations

The redistributed charge (RC) and redistributed charge and dipole (RCD) schemes were developed for handling the charges on boundary atoms by a classical simplification of the generalized hybrid orbital (GHO) method. Redistributed point charges were applied to mimic the auxiliary hybrid orbitals in GHO theory, and link atoms were used to represent the active hybrid orbital. The value of the redistributed charges and the values of charges on the second-tier molecular mechanical atoms were adjusted to preserve the M1 and M2 bond dipoles in the RCD method. The results show that it is critical to preserve charge and bond dipole and that it is important to use accurate MM point charge in QM/MM boundary treatment.