Spin-polarized calculations were performed, but the spinorbit interaction was not considered. For primitive cell calculations, the Brillouin zone was sampled by odd-number kpoint meshes with spacing less than 0.25 Å -1 , using the Monkhorst-Pack scheme. The electron wave functions were expanded in plane waves up to a kinetic energy cutoff of 650 eV, and the self-consistent field convergence energy was set to 10 - 4 eV. Full structural relaxations of the cell volume and atomic positions were performed until the residual forces on the ions converged to below 0.05 eV/Å. Subsequently, the cell volume and atomic positions were fixed, and the total energies were calculated using the tetrahedron method with Blöchl corrections. This computation condition is considered to be accurate enough for all materials in this study for discussing the stability of layered intercalation compounds.