Atomic charges in molecular mechanical force fields: A theoretical insight- art. no. 026703

Based on quantum theory of the Coulombic interactions between a molecule an d its surrounding molecules, a theoretical derivation is presented to obtai n an atomic charge model. The charge model shows that the appropriate atomi c charge, used for example in molecular mechanical force fields, is simply the average value of the electrostatic potential (ESP) derived charge for a n isolated molecule and that obtained for the molecule in the interaction s ystem. Computational scheme to calculate the ESP derived atomic charges of a molecule in the interaction system is presented. The method is applied to two common liquids with associated hydrogen bonds: water and methanol. The obtained theoretical atomic charges are similar to those found in the comm on interaction potential models, such as: SPC, TIP3P, OPLS, etc. However, f or methanol they differ considerably from those obtained using the restrain ed ESP method.