Figure shows the heat map of Ef obtained for the MC6-A stacking. All GICs of M = Li, K, Rb, Cs, Ca, Sr, and Ba, which were experimentally confirmed as stable GICs, have negative formation energies (blue color), indicating their stability in the simulations. We confirmed the same tendency in other stacking orders by their heat maps, as shown in Supplementary material. The result indicates that our calculations are in good agreement as they were inserted experimentally. Although the negative value of M = F was also demonstrated, the structure and bonding nature could be different from those of other GICs because the covalent bonding is considered more stable . Notably, the Ef for Sc, Y, Fr, and Rb is negative, although they have not been reported as GICs experimentally or computationally to date. According to the trends of other reported materials, these elements can also be intercalated into graphite to form new GICs. Notably, the GICs in Fig. had lower formation energies than Li-GIC and K-GIC (dashed red line). As mentioned previously in the proposed mechanism for the GIC processing using the Li-based molten alloy and LiCl-KCl molten salt methods , when the substitution of Li by intercalant M occurs, the M-GIC must be at least more stable than Li-GIC and K-GIC. Our calculation showed that Ca-, Sr-and Ba-GIC, which were reported in the Li-based molten alloy or LiCl-KCl molten salt method, were more stable than Li-GIC and K-GIC, supporting their thermodynamic substitution of Li or K.