金属Ni熔化前后结构变化的分子动力学模拟

Molecular Dynamics Simulation of the Structure Transformation before and after Ni Melting

使用Tight-binding势函数,对FCC-Ni升温熔化过程的结构变化进行了分子动力学模拟.在定压条件下模拟得到的Ni的熔点在1850K与1900K之间.计算得到了体系在各温度下的径向分布函数和配位数分布等静态结构信息以及动力学性质.计算得出的液体Ni的扩散系数在1900K时约为5.02×10-9m2·s-1,与实验数据相符.对液态体系中FCC短程有序结构可能发生的畸变以及由此导致的H-A键型变化进行了分析,结合配位体构型搜索和键对分析方法计算了各温度下不同短程有序结构的分布.计算表明,Ni在熔化之后仍保留有部分晶态短程结构,但发生了较大的畸变,同时液态中有少量的缺陷二十面体结构存在.而液体Ni中大多数的配位体的几何构型介于FCC与缺陷二十面体之间.

A series of molecular dynamics simulations for the structure transformation during heating and melting of FCC Ni have been performed with the Tight-binding potential developed by Cleft and Rosato. The simulated melting point of Ni at constant pressure condition is between 1850 K and 1900 K. The static structural informations, such as the radial distribution functions and the distributions of the coordination numbers, have been obtained during the simulation. The calculated diffusion coefficient of the liquid Ni is about 5.02×10^-9 m^2·s^-1 at 1900 K, which is consistent with the experimental result. The possible distortion of local structure of FCC crystal and the relevant changes of the types of the atom pairs （indexed by Honeycutt-Anderesen pair analysis technique） have been analyzed. The distributions of the short-range ordered （SRO） structures of FCC and defective icosahedra at different temperatures are calculated combining the local configuration search and H-A pair analysis methods. It is indicated that after melting a few SRO structures in FCC crystal are remained with distortion to a certain extent. A small quantity of the defective icosahedra in the liquid is also confirmed and their numbers are estimated. It suggested that the geometrical configurations of the local structure in liquid Ni are between the distorted cubooctahedron in FCC and the defective icosahedra.