Structural and energetic properties of nickel clusters: 2 <= N <= 150

[摘要] The four most stable structures of Ni-N clusters with N from 2 to 150 have been determined using a combination of the embedded-atom method in the version of Daw, Baskes, and Foiles, the variable metric/quasi-Newton method, and our own Aufbau/Abbau method. A systematic study of energetics, structure, growth, and stability of also larger clusters has been carried through without more or less severe assumptions on the initial geometries in the structure optimization, on the symmetry, or on bond lengths. It is shown that cluster growth is predominantly icosahedral with islands of fcc, tetrahedral and decahedral growth. For the first time in unbiased computations it is found that Ni-147 is the multilayer (third Mackay) icosahedron. Further, we point to an enhanced ability of fcc clusters to compete with the icosahedral and decahedral structures in the vicinity of N=79. In addition, it is shown that conversion from the hcp/anti-Mackay kind of icosahedral growth to the fcc/Mackay one occurs within a transition layer including several cluster sizes. Moreover, we present and apply different analytical tools in studying structural and energetic properties of such a large class of clusters. These include means for identifying the overall shape, the occurrence of atomic shells, the similarity of the clusters with, e.g., fragments of the fcc crystal or of a large icosahedral cluster, and a way of analysing whether the N-atom cluster can be considered constructed from the (N-1)-atom one by adding an extra atom. In addition, we compare in detail with results from chemical-probe experiment. Maybe the most central result is that first for clusters with N above 80 general trends can be identified.

[发布日期] 2004-11-01

[关键词] EMBEDDED-ATOM-METHOD;TRANSITION-METAL CLUSTERS;LENNARD-JONES CLUSTERS;MOLECULAR-DYNAMICS;MAGNETIC-MOMENTS;SHELL STRUCTURE;NI;BINDING;STATE;AG