Ni_n (n = 1 ~ 13) Clusters First Principle

Transition metal clusters have been widely used in the fields of material science, nano-technology, microelectronics, physical chemistry, life science and so on. The propertis of transiton metal clusters have attracted an increasing attention. The calculation for the Ni_n clusters can be seen in some literatures, but most of them were calculated by using an empirical potential. The studies by first-principle are much less due to the limit of computational efficiency. No determinate structures of Ni_n clusters can be compared with our calculated result except the pentagonal bipyramid structure of Ni₇ and the regular icosohedron structure of Ni₁₃. The result obtained by experiment is quite different from that predicted by theory, so our work has guidingeffect on the work in the future. In this paper, the possible structure of Ni_n( n = 1 ¹3) clusters are examined through first-principles calculations based on density functional theory. The equilibrium geometries and some properties of these clusters have been calculated. It is shown that the clusters do not mimic the bulk structure and undergo significant geometrical changes with size. The average bond length increases monotonically with size. The binding energy per atom increases monotonically with size except a knee point at n=7. It is found that Ni₅ and Ni₇ are more stable. The higher symmetry the clusters have, the more stable they are. At last, we calculate the ionization potentials of Ni_n (n=1～13) clusters. The calculated results are compared with those derived from experiments. The results reproduce the drastic oscillating behavior watched in experiments.