We also conducted calculation and decomposition of interaction energy at the SAPT2+(3)δMP2 level, which is arranged in Table . The interaction energies of complexes M + @C18 in obtained by DFT and SAPT are reasonably consistent, and their change trends with metal atomic numbers are exactly the same, thus confirming their reliability. The energy components extracted from SAPT2+(3)δMP2 calculations for exploring the nature of interaction between M + and C18 are plotted in Figure . It is seen that only the exchange-repulsion that essentially characterizes the steric effect contributes negatively to the binding, while all other components, including electrostatics, induction, and dispersion, promote formation of the complexation to different extents. Comparing different types of metal-doping, it is found that as the atomic number of M + increases, dispersion and induction effects between M + and C18 significantly increase and decrease, respectively, while electrostatics effect does not vary evidently and always contribute little to the complexation. Impressively, the induction effect mainly charactering polarization effect dominates the attractive part of the M + C18 interaction energy, and for the case of Li + -doping, it even contributes more than 93%. Although dispersion effect is not as important as induction effect for the studied interactions, its role should never be ignored, especially for M + with large atomic numbers. For example, contribution of dispersion effect to Cs + C18 binding is even comparable to that of induction effect. and. The corresponding TD-DFT results are employed to simulate the absorption spectra of the complexes, as shown in Figure .