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Density functional theory-based calculations have been used to demonstrate that the aplanarity of CO
groups in some carbonates such as dolomite, CaMg(CO
)
, aragonite, CaCO, and norsethite, BaMg(CO), is a ground-state property. This distortion stabilizes dolomite by ∼500 J mol
. Up to at least 6 GPa, the aplanarity of CO groups in dolomite is independent of pressure. In aragonite the aplanarity increases slightly on increasing pressure, while a significant tilting of the CO groups occurs. The calculations do not support previous findings of anomalously low values for the pressure derivative of the bulk moduli, 
, of aragonite and dolomite. Instead, the computed pressure dependences of the unit-cell volumes correspond to = 5.0 (5) for aragonite and = 4 (1) for dolomite, when fitted with a third-order Birch–Murnaghan equation-of-state.
groups in some carbonates such as dolomite, CaMg(CO
)
, aragonite, CaCO, and norsethite, BaMg(CO), is a ground-state property. This distortion stabilizes dolomite by ∼500 J mol
. Up to at least 6 GPa, the aplanarity of CO groups in dolomite is independent of pressure. In aragonite the aplanarity increases slightly on increasing pressure, while a significant tilting of the CO groups occurs. The calculations do not support previous findings of anomalously low values for the pressure derivative of the bulk moduli, 
, of aragonite and dolomite. Instead, the computed pressure dependences of the unit-cell volumes correspond to = 5.0 (5) for aragonite and = 4 (1) for dolomite, when fitted with a third-order Birch–Murnaghan equation-of-state.
