Where q i and q vac j are the atomic partial charges of the i th MM atom and the j th ML atom, respectively, while R MM i and R ML j are their coordinates. The dependency of q vac j on the coordinates of the ML atoms is indicated explicitly, as well as their in vacuo nature. The MM q i charges, on the other hand, are fixed parameters. E P ML/MM is the polarization energy, adjusted for the influence of surrounding dipoles using an effective dielectric constant ε and the polarizability of isolated atoms α free j :