The subgroup graph of SGs for calcite-like structures derived from the WTMetaD simulations is visualized in Fig. - alignment resembles the orthorhombic structure derived from XRD patterns. Note that the P bnm SG reported by Meyer is equivalent to P nma by axis conversion. Several authors have also performed DFT calculations based on these experimental results for orthorhombic systems. The monoclinic structures emerging in group D exhibit CO 3 2rotation associated with the stacking sequence in Ca 2+ sheets, as shown in Fig. ). The structure with C2/c SG is consistent with the four-layer structure determined by electron diffraction and ADF 9,10,57 of vaterite. A variety of structures involving CO 3 2rotation with different alignments in the stacking sequence of Ca 2+ sheets have been proposed by introducing rotational disorder in the hexagonal model (P 6 3 /mmc). These structures with monoclinic systems are attributed to different SGs and diversified by combinations of hexagonal arrangements through π/3 or 2π/3 rotations. Although only C2/c SG was found in this simulation, it is reasonable to consider that the low rotational barrier in the interlayer produces metastable polymorphs of other monoclinic crystals. These polymorphs were likely undetectable in WTMetaD simulations due to the very flat potential surface at high temperatures.