One of the methods to study the effects of intermolecular interactions is the perturbative approach, which employs a Rayleigh-Schrödinger perturbation theory. In this method, the electronic Hamiltonian of the supersystem is presented as a sum of the Hamiltonians of the isolated monomers ĤA and ĤB , and an intermolecular interaction operator V , gathering all the Coulomb interactions of all electrons and nuclei of one monomer with all electrons and nuclei of the other monomer as presented in equation (1). A starting point is the reference wavefunction ψ (0) assumed as a product of ground state wavefunctions of isolated monomers