高压下液态硅的结构和动力学特征
Structural and dynamic features of liquid Si under high pressure above the melting line minimum
摘要：
采用{ \it ab initio}方法模拟研究了硅熔体在10.2 ~ 24.3GPa压力范围内沿1150~K等温线的结构和动力学性质的变化。压力从10.2 GPa增加到16 GPa导致最近邻四面体有序度的强烈降低。扩散系数随原子体积的下降呈线性衰减，这与简单液态金属的理论预测一致，因此在对应于不同晶相边界的压力下没有显示出任何特征。速度自相关函数的傅立叶谱在20 GPa及更高压力下呈现双峰结构。这些特征频率与第二伪布里渊区中横向电流谱函数的峰值频率对应良好。两个几乎平坦的分支的短波长横模观察到的所有研究的压力。我们讨论了在纵向和横向分支的集体模式的特征频率的压力演化。
英文摘要：
We report an {\it ab initio} simulation study of changes in structural and dynamic properties of liquid Si at 7 pressures ranging from 10.2 GPa to 24.3 GPa along the isothermal line 1150~K, which is above the minimum of the melting line. The increase of pressure from 10.2 GPa to 16 GPa causes strong reduction in the tetrahedral ordering of the most close neighbors. The diffusion coefficient shows a linear decay vs drop in atomic volume, that agrees with theoretical prediction for simple liquid metals, thus not showing any feature at the pressures corresponding to the different crystal phase boundaries. The Fourier-spectra of velocity autocorrelation function shows two-peak structure at pressures 20 GPa and higher. These characteristic frequencies correspond well to the peak frequencies of the transverse current spectral function in the second pseudo-Brillouin zone. Two almost flat branches of short-wavelength transverse modes were observed for all the studied pressures. We discuss the pressure evolution of characteristic frequencies in the longitudinal and transverse branches of collective modes.
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