Theoretical study on the structure and dynamics of liquids which show metal-nonmetal transitions

在本研究项目中，我们通过研究液态金属的结构和动力学性质，对液态金属中金属-非金属转变的微观机制进行了模拟研究。我们研究并澄清了以下问题：(1)非金属流体汞在临界点附近的静态结构可用有效的Lennard-Jones对势能很好地描述。利用有效对势的分子动力学(MD)模拟研究了流体汞在临界点附近的动态结构，结果表明，与最近的非弹性X射线散射实验相比，动力学结构因子、色散关系和声速也得到了很好的描述。(2)高温高压下，液态磷发生了一级液-液相变。我们用从头算MD模拟研究了这种液态磷的动力学性质，发现了P_4分子的振动模和声速，为以后的实验提供了参考。(3)研究了压力引起的液态碳的结构和电子态的变化，阐明了压力引起结构变化的微观机制。(4)用从头算方法研究了液态In_2Te_3和As_2S_3等液态混合物的结构和电子态，以阐明半导体-金属相变的机制。(5)用从头算MD方法研究了液态Ge-Sn和Ge-Si合金等14族液态混合物的结构和电子性质。

In this research project we have carried out simulation studies to clarify the microscopic mechanism of metal-nonmetal transitions in liquid metals by investigating the structural and dynamical properties of these liquids. We have studied and clarified the following problems :(1)The static structure of nonmetallic fluid mercury near the critical point is known to be well described by the effective Lennard-Jones-type pair potential. We have investigated the dynamic structure of fluid mercury near the critical point by the molecular-dynamics (MD) simulations using the effective pair potential and shown that the dynamical structure factor, the dispersion relation and the sound velocity are also well described in comparison with the recent inelastic x-ray scattering experiments.(2)It is known that there occurs a first-order liquid-liquid phase transition in liquid phosphorus at high temperatures and high pressures. We have studied the dynamical properties of such liquid phosphorus by ab initio MD simulations and found the vibration mode of P_4 molecules and the sound velocity, which are suggestive for future experiments.(3)We have investigated the pressure-induced changes in the structure and electronic states of liquid carbon, and clarified the microscopic mechanism of the pressure-induced structural change, in particular the origin of the maximum melting point.(4)We have investigated by ab initio MD simulations the structure and electronic states of liquid mixtures such as liquid In_2Te_3 and As_2S_3 to clarify the mechanism of semiconductor-metal transition.(5)We have studied the structural and electronic properties of group 14 liquid mixtures such as liquid Ge-Sn and Ge-Si alloys by ab initio MD simulations.