Here, E Zn@CS stands for the energy of a given Zn(II) cluster, E CS for the energy or a preorganized coordination shell without Zn(II), E Zn is the energy of a Zn(II) atom and E Li is the energy of the isolated ligands. This scheme is similar to the one previously used to evaluate metal-binding energies for serum-transferrin , albeit more complete since we introduce the penalty paid for forming a given coordination shell. A particular feature of our calculations is that the basis sets of the Zn(II) cluster are always present in all calculations. That is, when removing atoms from the cluster to take into account the different terms specified before we use "ghost atoms", namely, we keep their normal basis functions and numerical integration grid points but no nuclear charge or electrons for the ghost atoms.