分子动力学方法研究金属Ti中He小团簇的迁移

采用分子动力学方法模拟了不同温度下He原子及He团簇在金属Ti中的迁移特性,并计算了扩散前系数和激活能. 研究发现这种扩散的各向异性非常显著,具体表现在He原子及He团簇在不同方向上扩散系数的前系数完全不同,但它们的激活能却相同. 研究表明:在预测金属中He的扩散行为时,必须采用动态模拟方法才能得到准确的前系数,仅仅考虑势垒的静态模拟方法是不行的. 另外,还发现一个不同于直觉的现象,即较低温度下He二聚物的扩散系数比单个He原子的扩散系数大;此外,在所模拟的温度范围内Arrhenius方程能够很好地描述它们的扩散. 这说明动力学模拟对预测金属中He的扩散行为具有重要的意义. 关键词： 分子动力学 扩散系数 各向异性 氦

Molecular dynamics study of small helium cluster diffusion in titanium

The diffusions of He atom and small He clusters in Ti at different temperatures are simulated by molecular dynamics. The prefactors and the activation energies of diffusion coefficients are calculated. It can be concluded that the diffusion is anisotropic. Simulations show that prefactors of diffusion coefficients are different from those of He species diffusing in different directions, but the activation energies are the same. The result demonstrates that it is insufficient to predict the diffusion behavior of He in metal when only the energy barrier in static lattice is considered. Dynamics calculations are necessary to obtain the correct prefactors. Another counterintuitive observation is that He-dimer migrates more quickly than single He atom does at room temperature. The results emphasize the importance of dynamics simulations in predicting diffusion behavior of He in metals.