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首页> 外文期刊>Physical Review, B. Condensed Matter >First-principles study of the ferroelastic phase transition in CaCl2 - art. no. 134104
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First-principles study of the ferroelastic phase transition in CaCl2 - art. no. 134104

机译：CaCl2中铁弹性相变的第一性原理研究-艺术没有。 134104

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First-principles density-functional calculations within the local-density approximation and the pseudopotential approach are used to study and characterize the ferroelastic phase transition in calcium chloride (CaCl2). In accord with experiment, the energy map of CaCl2 has the typical features of a pseudoproper ferroelastic with an optical instability as ultimate origin of the phase transition. This unstable optic mode is close to a pure rigid unit mode of the framework of chlorine atoms and has a negative Gruneisen parameter. The ab initio ground state agrees fairly well with the experimental low-temperature structure extrapolated at 0 K. The calculated energy map around the ground state is interpreted as an extrapolated Landau free energy and is successfully used to explain some of the observed thermal properties. Higher-order anharmonic couplings between the strain and the unstable optic mode, proposed in previous literature as important terms to explain the soft-phonon temperature behavior, are shown to be irrelevant for this purpose. The linearized augmented plane wave method is shown to reproduce the plane-wave results in CaCl2 within the precision of the calculations, and is used to analyze the relative stability of different phases in CaCl2 and the chemically similar compound SrCl2. [References: 40]
机译：使用局部密度近似中的第一性原理密度函数计算和拟势方法来研究和表征氯化钙（CaCl2）中的铁弹性相变。根据实验，CaCl2的能谱具有伪适当的铁弹性体的典型特征，其光学不稳定性是相变的最终起源。这种不稳定的光学模式接近于氯原子框架的纯刚性单元模式，并具有负的Gruneisen参数。从头算起的基态与在0 K处外推的实验低温结构非常吻合。基态周围的计算能量图被解释为外推的Landau自由能，并成功地用于解释一些观察到的热性质。先前的文献中提出的应变和不稳定光学模式之间的高阶非谐耦合被认为与该目的无关，后者是解释软声子温度行为的重要术语。显示了线性化增强平面波方法，可以在计算精度范围内重现CaCl2中的平面波结果，并用于分析CaCl2和化学相似的化合物SrCl2中不同相的相对稳定性。 [参考：40]

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