Preparation: Periodic information from any source is used to generate a finite cluster of molecules. The center of mass of the "central molecule" is used as the cluster origin. All molecules within a cutoff distance from the origin are included. A point charge and a LJ parameter is added for every cluster atom. Additional point charges (background charges) to account for the periodic electrostatics are added slightly above the cluster surface and later fitted to reproduce the electric field and electrostatic potential at the atom positions of the "central molecule".