Key Laboratory of Computational Physics, Yibin University, Yibin 644000, China.
Centre for Experimental and Teaching Resource Management, Yibin University, Yibin 644000, China.
J Chem Phys. 2014 Mar 21;140(11):114505. doi: 10.1063/1.4868550.
Molecular dynamics simulations were applied to study the structural and transport properties, including the pair distribution function, the structure factor, the pair correlation entropy, self-diffusion coefficient, and viscosity, of liquid iron under high temperature and high pressure conditions. Our calculated results reproduced experimentally determined structure factors of liquid iron, and the calculated self-diffusion coefficients and viscosity agree well with previous simulation results. We show that there is a moderate increase of self-diffusion coefficients and viscosity along the melting curve up to the Earth-core pressure. Furthermore, the temperature dependencies of the pair correlation entropy, self-diffusion, and viscosity under high pressure condition have been investigated. Our results suggest that the temperature dependence of the pair correlation entropy is well described by T(-1) scaling, while the Arrhenius law well describes the temperature dependencies of self-diffusion coefficients and viscosity under high pressure. In particular, we find that the entropy-scaling laws, proposed by Rosenfeld [Phys. Rev. A 15, 2545 (1977)] and Dzugutov [Nature (London) 381, 137 (1996)] for self-diffusion coefficients and viscosity in liquid metals under ambient pressure, still hold well for liquid iron under high temperature and high pressure conditions. Using the entropy-scaling laws, we can obtain transport properties from structural properties under high pressure and high temperature conditions. The results provide a useful ingredient in understanding transport properties of planet's cores.
采用分子动力学模拟方法研究了液态铁在高温高压条件下的结构和输运性质，包括配分函数、结构因子、对关联熵、自扩散系数和黏度。我们的计算结果再现了液态铁的实验确定的结构因子，计算得到的自扩散系数和黏度与先前的模拟结果吻合较好。结果表明，自扩散系数和黏度沿着熔化曲线在地球核压力下适度增加。此外，还研究了高压条件下对关联熵、自扩散和黏度随温度的依赖性。结果表明，对关联熵的温度依赖性很好地符合 T(-1)标度，而自扩散系数和黏度的 Arrhenius 定律很好地描述了高压下的温度依赖性。特别是，我们发现 Rosenfeld [Phys. Rev. A 15, 2545 (1977)]和 Dzugutov [Nature (London) 381, 137 (1996)]提出的适用于常压下液态金属自扩散系数和黏度的熵标度律，在高温高压条件下仍然适用于液态铁。利用熵标度律，可以从高压高温条件下的结构性质得到输运性质。这些结果为理解行星核的输运性质提供了有用的信息。
