This review paper describes the structure of amorphous calcium carbonate (ACC), which we recently investigated by means of molecular dynamics simulation. Our simulation suggested that the structure of ACC resembled that of vaterite. However, adding Mg2+ ions disrupted the formation of the vaterite-like structure in ACC. Moreover, the structure of ACC in the presence of Mg2+ ions approached that of monohydrocalcite when the concentration of H2O molecules was high. The relationship between the simulated structure of ACC and the structure of calcium carbonate crystals nucleated through the formation of ACC particles in real systems is discussed. In addition, the relationship between the present simulation results and the formation of aragonite thin-film on the matrices of polyvinyl alcohol in the presence of Mg2+ ions is also discussed.
