冷却速率对Lennard-Jones体系凝固过程中结构与动力学性质的影响

用分子动力学模拟方法研究了五种不同冷却速率对Lennard-Jones体系凝固过程中结构与动力学性质的影响。采用两种不同的方法来确定玻璃转变温度Tg，并且对结晶温度Tc、径向分布函数g(r)、均方位移函数MSD与扩散系数D、平均配位数进行比较分析。结果表明：冷却速率影响Lennard-Jones体系凝固过程中的结构。当使用足够高的冷却速率冷却时，体系发生玻璃化转变，而且冷却速率越快，玻璃转变温度越高；当冷却速率较小时，体系形成晶体，而且冷却速率越慢，结晶温度越高，结晶程度也越高。同时发现，冷却速率对扩散系数和平均配位数也有很大影响，二者在体系发生玻璃转变时都有一个缓变的过程，表明了过冷液相区的存在。

Effects of cooling rates on structures and kinetic properties during solidification process of the Lennard-Jones system

A molecular dynamics simulation study was performed for the effects of five different rates on structures and kinetic properties during solidification process of the Lennard-Jones system. Glass transition temperature Tg was measured by using two different methods, and the crystallization temperature Tc, the radial distribution function, the mean square displacement MSD, the diffusion coefficient D and the mean coordination number were used to compare and analyze. The results show that the cooling rate plays a critical role on structures during solidification process of the Lennard-Jones system. As the cooling rate being high enough, the system will be transferred into glass, and the greater the cooling rate, the higher the glass transition temperature. As the cooling rate being smaller, the system will be crystallized, and the slower the cooling rate, the higher the crystallization temperature, and the higher the degree of crystallization. At the same time, it is found that the diffusion coefficient and the mean coordination number are largely influenced by cooling rates, and both have a slow graded process of the glass transition occurred in the system, which shows the existence of supercooled liquid region.