Winkler B, Zemann J, Milman V
Institut fur Geowissenschaften/Kristallographie, Universitat Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany.
Acta Crystallogr B. 2000 Aug;56(Pt 4):648-53. doi: 10.1107/s0108768100003621.
Density functional theory-based calculations have been used to demonstrate that the aplanarity of CO3 groups in some carbonates such as dolomite, CaMg(CO3)2, aragonite, CaCO3, and norsethite, BaMg(CO3)2, is a ground-state property. This distortion stabilizes dolomite by approximately 500 J mol(-1). Up to at least 6 GPa, the aplanarity of CO3 groups in dolomite is independent of pressure. In aragonite the aplanarity increases slightly on increasing pressure, while a significant tilting of the CO3 groups occurs. The calculations do not support previous findings of anomalously low values for the pressure derivative of the bulk moduli, B', of aragonite and dolomite. Instead, the computed pressure dependences of the unit-cell volumes correspond to B' = 5.0 (5) for aragonite and B' = 4(1) for dolomite, when fitted with a third-order Birch-Murnaghan equation-of-state.
基于密度泛函理论的计算已被用于证明，在一些碳酸盐中，如白云石（CaMg(CO3)2）、文石（CaCO3）和水碳镁石（BaMg(CO3)2），CO3基团的非平面性是一种基态性质。这种畸变使白云石的稳定性提高了约500 J mol(-1)。在至少6 GPa的压力下，白云石中CO3基团的非平面性与压力无关。在文石中，随着压力增加，非平面性略有增加，同时CO3基团发生显著倾斜。这些计算不支持先前关于文石和白云石的体模量压力导数B'异常低值的发现。相反，当用三阶Birch-Murnaghan状态方程拟合时，计算得到的晶胞体积的压力依赖性对应于文石的B' = 5.0 (5)和白云石的B' = 4(1)。
