The energies of the sampled vaterite-like structures are plotted relative to the calcite structure in Fig. . The results calculated from the proposed vaterite crystal structures are also shown in Fig. . The structures with P 2 1 /c and P nma SGs in group C have higher energies of about 5 and 7 kJ/mol than the structure with C2/c SG, which is a probable vaterite structure. The P 1 structure has a higher energy of approximately 10 kJ/mol relative to calcite. These structures are attributed to metastable states during vaterite formation from ACC.