Consequently, MESP significantly impacts the entropy level of the association complex. As the molecules come into close proximity, the MESP is perturbed and deviates from the MESP of the isolated molecule, influenced by factors such as charge transfer, polarization, and dispersion contributions to the energy perturbation. These contributions can sometimes exceed the Columbic energy, indicating that the final step of the reaction cannot be solely described by electrostatic energy . However, if there is no bond cleavage or bond formation during this reaction step, the stability of the complex formed between the drug and the active site of the receptor can be correlated with extreme MESP values. In such cases, these MESP values can serve as an expression of the drug's activity.