Molecular dynamics simulation of the phase transition between calcite and CaCO3-II
Molecular dynamics simulation of the phase transition between calcite and CaCO3-II
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DOI：
10.1088/0953-8984/21/27/275403
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发表时间：
2009-07
期刊：
影响因子：
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通讯作者：
J. Kawano;A. Miyake;N. Shimobayashi;M. Kitamura
中科院分区：
文献类型：
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作者：
J. Kawano;A. Miyake;N. Shimobayashi;M. Kitamura
采用分子动力学（MD）方法模拟了高压下碳酸钙（CaCO 3-II，P21/c）的相变过程。在300-800 K温度范围内，在8 GPa左右的压力下再现了方解石向CaCO 3-II的转变。这种转变是一阶和可逆的MD计算中，除了运行在300 K，其中存在一个小的滞后。方解石和CaCO 3-II之间的相界的dP/dT曲线的斜率在300 K时为负，并在600 K左右变为正，这通过分析焓变来证实。在低于转变压力时，P21/c结构出现，其取向随时间在三个位置之间转换，导致结构整体保持不变。P21/c结构随温度的升高与CaCO 3-II结构相似。P21/c结构的存在及其在转变压力以下的取向转变是导致边界dP/dT曲线斜率随温度升高由负变正的原因，因为这种转变增加了方解石的熵，导致稳定场的扩大。
Molecular dynamics (MD) simulation of calcium carbonate at high pressure was performed to understand the phase transition between calcite and CaCO3-II (P 21/c). In the 300–800 K temperature range, the transition of calcite to CaCO3-II was reproduced at a pressure of around 8 GPa. This transition is of first order and reversible in the MD calculations except for runs at 300 K where a small hysteresis exists. The slope of the dP/dT curve at the phase boundary between calcite and CaCO3-II is negative at 300 K and turns positive at around 600 K, which was confirmed by analyzing the enthalpy change. Just below the transition pressure, the P 21/c structure appears and its orientation switches among three positions with time, resulting in the maintenance of the structure as a whole. The P 21/c structure resembles the structure of CaCO3-II on an increase of temperature. It can be suggested that the existence of the P 21/c structure and the switching of its orientation just below the transition pressure are responsible for the change of the slope of the dP/dT curve at the boundary from negative to positive on an increase of temperature, because the switching increases entropy and results in an expansion of the stability field of calcite.