Lattice dynamics and thermodynamics of molybdenum from first-principles calculations.
Lattice dynamics and thermodynamics of molybdenum from first-principles calculations.
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DOI：
10.1021/jp9073637
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发表时间：
2010-01
期刊：
影响因子：
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通讯作者：
Zhao-Yi Zeng;Cui-E. Hu;L. Cai;Xiang-Rong Chen;F. Jing
中科院分区：
文献类型：
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作者：
Zhao-Yi Zeng;Cui-E. Hu;L. Cai;Xiang-Rong Chen;F. Jing
我们使用密度函数理论计算了钼（MO）的相变的相变，弹性常数，完整的声子分散曲线和钼（MO）的热性能。 MO在最高703 +/- 19 GPA的以身体为中心（BCC）结构中稳定，然后在零温度下转换为以面部为中心的闭合（FCC）结构。在高温和压力下，MO的FCC相比BCC相更稳定。计算出的声子分散曲线与实验非常相符。在压力下，我们沿着TA分支的H-P捕获了大量软化。当体积被压缩到7.69 a（3）时，沿TA分支中H-P的频率将软化至虚发生频率，表明结构不稳定。当压力增加时，FCC MO上的声子计算通过促进沿伽马到X和伽玛的频率从虚构到真实的L对称线来预测稳定性。还研究了状态的热方程。从热膨胀系数和热量容量中，我们发现准毛电近似仅在零压力下的熔点有效。但是，在压力下，有效性可以扩展到更高的温度。
We calculated the phase transition, elastic constants, full phonon dispersion curves, and thermal properties of molybdenum (Mo) for a wide range of pressures using density functional theory. Mo is stable in the body-centered-cubic (bcc) structure up to 703 +/- 19 GPa and then transforms to the face-centered close-packed (fcc) structure at zero temperature. Under high temperature and pressure, the fcc phase of Mo is more stable than the bcc phase. The calculated phonon dispersion curves accord excellently with experiments. Under pressure, we captured a large softening along H-P in the TA branches. When the volume is compressed to 7.69 A(3), the frequencies along H-P in the TA branches soften to imaginary frequencies, indicating a structural instability. When the pressure increases, the phonon calculations on the fcc Mo predict the stability by promoting the frequencies along Gamma to X and Gamma to L symmetry lines from imaginary to real. The thermal equation of state was also investigated. From the thermal expansion coefficient and the heat capacity, we found that the quasiharmonic approximation was valid only up to about melting point at zero pressure. However, under pressure, the validity can be extended to a much higher temperature.