Structure stability and configuration evolution of Aln (n=3, 4, 6, 13, 19) clusters

Abstract

Using a first-principles pseudo-potential plane wave method, the geometrical and electronic structures of Al n (n=3, 4, 6, 13, 19) clusters with different configurations have been calculated. Several parameters such as the binding energy E b and the HOMO-LUMO energy gap ∆E H-L have been adopted to characterize and analyze the structure stability of these clusters, and their configuration evolutions are also investigated by linear synchronous transit (LST) method. It is demonstrated that the stable configurations of Al 3 , Al 4 , Al 6 , Al 13 , Al 19 clusters are triangle, rhombus, octahedron, icosahedron and double icosahedron, respectively. For Al 6 and Al 19 clusters there are metastable structures of parallelogram and octahedron, respectively, whereas in the Al 3 , Al 4 and Al 13 clusters, no metastable configuration is validated. There exist a large energy gap and a low energy barrier between the octahedron and the parallelogram of the Al 6 cluster, so the transformation from its metastable to stable structures is rather easy. By contrast, a small energy gap and a high energy barrier between the stable and metastable structures of Al 19 cluster mean its configuration evolution from the octahedron to the double icosahedron occurs hardly, therefore the metastable octahedron configuration of Al 19 cluster can be extensively detected in experiments and simulations.As a special phase in the process of transformation from atoms or molecules to bulk materials, a cluster represents an original state of a condensed matter. For studies on structures and properties of clusters it is a basic problem to investigate how atoms or molecules form clusters and what changes will take place during the configuration evolution of clusters. Recently Al n clusters attract many researchers' attention because of its simple electronic structures and unique conductive characters, i.e. an obvious variation of its conductibility from an isolator to a conductor with the addition in atoms of Al n cluster. In the past two decades, a lot of theoretical [1][2][3][4][5][6] and experimental [7,8] researches have 386 Science in China Series E: Technological Sciences been done. Liu et al. [1] simulated the formation and evolution of Al n clusters during rapid cooling processes of liquid metal systems by a molecular dynamics (MD) method. The results demonstrated that only an icosahedral atom aggregations of (12 0 12 0) related to the 1551 bond-types and their combinations could easily grow and have inheritable characters, and no high symmetrical cuboctahedrons or decahedrons were detected. Using genetic algorithm, Bian et al. [2] investigated the Bernal polyhedrons of aluminum and found the stable structure of Al 6 cluster is an octahedron. By using Gaussian program based on density functional theory (DFT) and generalized gradient approximation (GGA), Wang et al. [3] also investigated the geometrical structures and their energy levels of small clusters of Al n (n=2-7), and validated that the shapes of Al n clusters are planar structures as n≤5 and...

Nanosolids, Slushes, and Nanoliquids: Characterization of Nanophases in Metal Clusters and Nanoparticles

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“…14,61,72,75,80,83,85 We find that Al 13 has a very large energy gap (1.01 eV) between the GM and the second lowest energy isomer, and ab initio calculations indicate that there is a very high energy barrier between the two lowest energy structures. 80 Therefore, Al 13 has extraordinary structural stability. It may therefore be called a magic structure or, since it also keeps its structure in chemical reactions, a superatom.…”

“…The distinction between clusters and nanoparticles is not strict, and we use the generic name particles to refer to both of them. Aluminum particles have been of great experimental ,− ,− and theoretical ,,,,,,,,,− interest for decades. Their melting has recently been the subject of extensive experimental ,− and theoretical study. ,,,,,,− Jarrold et al used multicollision-induced dissociation to measure the heat capacities of Al n cationic clusters with n = 16−48, 31−38, 49−63, and 63−83 .…”

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“…Following the work of Rao [7] and our former study [5][6] , the original models of stable Al n (n = 6,7,13) clusters are firstly constructed, as shown in Fig. 1, in which the initial Al-Al bond distance is set to d=2.863 Å.…”

“…2 (d) respectively. To these metastable structures, we have reported them to be changed easily into incompact structure [5] . Moreover they are self-adjustment from "energy valley B" to resultants in the configuration evolution except the reaction as Fig.…”