Structure and stability of copper clusters: A tight-binding molecular dynamics study

Abstract

In this paper we propose a tight-binding molecular dynamics with parameters fitted to firstprinciples calculations on the smaller clusters and with an environment correction, to be a powerful technique for studying large transition/noble metal clusters. In particular, the structure and stability of Cun clusters for n = 3−55 are studied by using this technique. The results for small Cun clusters (n = 3 − 9) show good agreement with ab initio calculations and available experimental results. In the size range 10 ≤ n ≤ 55 most of the clusters adopt icosahedral structure which can be derived from the 13-atom icosahedron, the polyicosahedral 19-, 23-, and 26-atom clusters and the 55-atom icosahedron, by adding or removing atoms. However, a local geometrical change from icosahedral to decahedral structure is observed for n = 40 − 44 and return to the icosahedral growth pattern is found at n = 45 which continues. Electronic "magic numbers" (n = 2, 8, 20, 34, 40) in this regime are correctly reproduced. Due to electron pairing in HOMOs, even-odd alternation is found. A sudden loss of even-odd alternation in second difference of cluster binding energy, HOMO-LUMO gap energy and ionization potential is observed in the region n ∼ 40 due to structural change there. Interplay between electronic and geometrical structure is found.

Structural and energetic analysis of copper clusters: MD study of Cu n (n = 2-45)

“…55,[61][62][63] The average binding energy per atom in the cluster may be, therefore, expressed as a function of the cluster size, [64][65][66] (2) where the coefficients E v , E s , and E c correspond to the volume, surface, and curvature energies of the particles forming the cluster, respectively, and E e defines the energy origin. 67 Fitting the data according to equation (2) gives 5.82, 11.45, 5.64 and 6.6 10 -5 eV/atom, respectively.…”

All-electron relativistic calculations on hydrogen atom adsorption onto small copper clusters

“…1 are in good agreement with available previous works [31][32][33][34][35][36][37]. Then, based on the optimized lowest energy structures of Cu n clusters, we performed an extensive lowest energy structures search for hydrogen atom bonding onto Cu n cluster according to the ways described in ''Computational method and cluster model''.…”

“…In this work, we obtained the initial structures by two ways. First, considering previous studies on the configurations of pure copper clusters [31][32][33][34][35][36][37], we optimize the structures of pure Cu n cluster by using the same method and same parameters. On the basis of the optimized equilibrium geometries of pure copper clusters, we obtain the initial structures of Cu n H clusters by adding hydrogen atom directly on each possible non-equivalent site of Cu n cluster.…”

Positive XPS binding energy shift of supported CuN-clusters governed by initial state effects

“…Reasons for an increased initial state energy, i.e. orbital energy, might generally be related to a change of geometry and enhanced molecular character of the clusters due to bond length reduction [17][18][19][20][21] and hybridization. Charge transfer from the cluster to the substrate might also contribute to the increased initial state energy of the supported clusters.…”