Department of Geosciences, New York Center for Computational Sciences, Stony Brook University, Stony Brook, NY 11794-2100, USA.
Proc Natl Acad Sci U S A. 2010 Apr 27;107(17):7646-51. doi: 10.1073/pnas.0910335107. Epub 2010 Apr 9.
Experimental studies established that calcium undergoes several counterintuitive transitions under pressure: fcc --> bcc --> simple cubic --> Ca-IV --> Ca-V, and becomes a good superconductor in the simple cubic and higher-pressure phases. Here, using ab initio evolutionary simulations, we explore the behavior of Ca under pressure and find a number of new phases. Our structural sequence differs from the traditional picture for Ca, but is similar to that for Sr. The beta-tin (I4(1)/amd) structure, rather than simple cubic, is predicted to be the theoretical ground state at 0 K and 33-71 GPa. This structure can be represented as a large distortion of the simple cubic structure, just as the higher-pressure phases stable between 71 and 134 GPa. The structure of Ca-V, stable above 134 GPa, is a complex host-guest structure. According to our calculations, the predicted phases are superconductors with Tc increasing under pressure and reaching approximately 20 K at 120 GPa, in good agreement with experiment.
实验研究表明，钙在压力下经历了几个违反直觉的转变：fcc → bcc → 简单立方 → Ca-IV → Ca-V，并在简单立方和更高压力相变为良好的超导体。在这里，我们使用从头算演化模拟，探索了钙在压力下的行为，并发现了一些新的相。我们的结构序列与钙的传统图像不同，但与锶相似。β-锡（I4(1)/amd）结构，而不是简单立方，预计在 0 K 和 33-71 GPa 时是理论基态。这种结构可以表示为简单立方结构的大变形，就像在 71 到 134 GPa 之间稳定的高压相一样。在 134 GPa 以上稳定的 Ca-V 结构是一种复杂的主体-客体结构。根据我们的计算，预测的相是超导相，随着压力的增加而升高，在 120 GPa 时达到约 20 K，与实验结果非常吻合。
