The derived results show that when the partial atomic charges are used to simulate the intermolecular Coulomb interaction, the appropriate charge value on an atom corresponds to the average of the electrostatic potential (ESP) derived charge for an isolated molecule and that obtained for the molecule in the interaction system. Therefore, the derived charge model is environmental dependent. Neither the charges from an isolated molecule nor those from the molecule in the interaction system could be good approximations to the calculation of intermolecular Coulomb interaction. Since atomic charges are widely used in MM force fields to simulate the Coulomb interaction between the molecules, we believe that the derived charge model is helpful in the development of accurate MM force field methods.

As an application of the charge model, the partial atomic charges on water and methanol molecules suitable for liquid simulations are calculated and compared with those from the widely used MM force field models. For water, the obtained atomic charges are similar to those in the empirical SPC and TIP3P models. For methanol, the calculated atomic charges are close to those in the empirical OPLS model.

References

Yaoquan Tu and Aatto Laaksonen.
Atomic Charges in molecular mechanical force fields: A theoretical insight
Physical Review E 64 (2-2), 6703-6710 (2001).