in which q i is the partial atomic charge (Drude oscillators and lone pairs included) and r p is the position of the particle. The vacuum permittivity ( 0 ) was set to 8.8541878128 × 10 -12 F m -1 . By using this approach, we were able to account for heterogeneous electronic microenvironments at the PET surfaces, allowing for a better description of the electrostatic potential.