高压下钙的简单立方相的杂化泛函研究
Hybrid Functional Study Rationalizes the Simple Cubic Phase of Calcium at High Pressures
摘要：
自1984年以来，简单立方（SC）相长期以来被实验确定为元素钙（Ca）的高压相III。然而，最近的密度泛函计算内半局域近似表明，该SC相是结构上不稳定的表现出严重的虚声子，并在能量上不稳定相对于理论体心tetraxinI 41/amd结构的压力范围内相III。这些计算引起了广泛的争论SC阶段的有效性。在这里，我们已经重新审视了SC结构进行更精确的密度泛函计算内的混合泛函海德-Scuseria-Erhzerhof（HSE）和PBE 0。我们的计算能够从根本上合理的SC结构的相稳定性在所有其他已知的阶段的证据，其实际的能量稳定性高于33 GPa和其内在的动力学稳定性，而不显示任何假想的声子在整个压力范围内的研究。我们进一步确定了长期以来的理论I41/amd结构在进入SC相之前在一个狭窄的压力范围内保持稳定，并且实际上是最近在低温14 K下合成的实验Ca-III'的结构，这得到了我们的模拟X射线衍射图案与实验数据之间的极好的一致性的支持。我们的研究结果揭示了精确的电子交换能在正确描述Ca的势能中所起的关键作用。
英文摘要：
Simple cubic (SC) phase has been long experimentally determined as the high-pressure phase III of elemental calcium (Ca) since 1984. However, recent density functional calculations within semi-local approximation showed that this SC phase is structurally unstable by exhibiting severely imaginary phonons, and is energetically unstable with respect to a theoretical body-centered tetragonal I41/amd structure over the pressure range of phase III. These calculations generated extensive debates on the validity of SC phase. Here we have re-examined the SC structure by performing more precise density functional calculations within hybrid functionals of Heyd-Scuseria-Erhzerhof (HSE) and PBE0. Our calculations were able to rationalize fundamentally the phase stability of SC structure over all other known phases by evidence of its actual energetic stability above 33 GPa and its intrinsically dynamical stability without showing any imaginary phonons in the entire pressure range studied. We further established that the long-thought theoretical I41/amd structure remains stable in a narrow pressure range before entering SC phase and is actually the structure of experimental Ca-III' synthesized recently at low temperature 14 K as supported by the excellent agreement between our simulated X-ray diffraction patterns and the experimental data. Our results shed strong light on the crucial role played by the precise electron exchange energy in a proper description of the potential energy of Ca.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
