First-principles calculations were performed on the obtained layered intercalation compounds and host-only structures. Structural relaxations through simulations based on DFT were performed on the initial structures using the plane-wave basis projector augmented wave method implemented in the VASP code. For the simulation of the layered compounds, van der Waals dispersion (vdW) forces have to be implemented in the simulation. To consider vdW interaction, we systematically tested various vdW density functional methods for the GICs as the reference, confirming the reproducibility of crystal structures and the validity of the formation energies. The results are listed in Table . Consequently, we selected the rev-vdW-DF2 method proposed by Hamada, which was implemented using the algorithm of Román-Pérez and Soler 64 because both errors were the lowest.