Evolution of (GaAl) n Clusters and Chemisorptions of H 2 on (GaAl) n Clusters
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Evolution of (GaAl)n Clusters and Chemisorptions of H2 on (GaAl)n Clusters Ling Guo
Received: 18 April 2012 / Published online: 21 November 2012 Ó Springer Science+Business Media New York 2012
Abstract The growth behavior of (GaAl)n (n = 1–12) and the chemisorptions of hydrogen on the ground state geometries have been studied with the three-parameter hybrid generalized gradient approximation due to Becke-Lee–Yang–Parr (B3LYP). The dissociation energy, the second-order energy differences, and the HOMO– LUMO gaps indicate that the magic numbers of the calculated (GaAl)n clusters are n = 4 and 6. To my knowledge, this is the first time that a systematic study of chemisorptions of hydrogen on gallium aluminum clusters. The onefold top site of aluminum atom is identified to be the most favorable chemisorptions site for one hydrogen chemisorptions on most (GaAl)n clusters. In general, dissociative chemisorptions of a hydrogen molecule on a top site of aluminum atom is found common for all sizes clusters considered here except for (GaAl)n (n = 1–3) clusters. The stability of the (GaAl)nHm complexes shows that both large second-order difference and large fragmentation energies for (GaAl)10H2 and (GaAl)11H2 make these species behaving like magic clusters. Keywords (GaAl)n Cluster Hydrogenated gallium aluminum cluster Stability Electronic properties Introduction Bulk phase bimetallic systems provide a matter of increasing interest in pure and applied materials sciences and traditional fields of physics and chemistry. In catalytic chemistry and chemical engineering, real catalysts mainly consist of a heterometallic or bimetallic system, which can profoundly enhance reactivity and selectivity. Thus, to get a deeper understanding of the microscopic behavior of these species, the study of bimetallic or so-called alloy clusters provides a suitable tool, L. Guo (&) School of Chemistry and Material Science, Shanxi Normal University, Linfen 041004, China e-mail: [email protected]
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since cluster science enables one to investigate chemical and physical properties starting from a single atom or molecule toward bulk phase as a function of size. Therefore, in the last decades a number of studies of bimetallic clusters and diatomic molecules have been performed. [1–4]. Among the candidate systems to have been considered, the bimetallic gallium aluminum clusters have been the topic of some experimental and theoretical studies. For experiment [5], the GaAl clusters are generated by pulsed laser ablation of a liquid aluminum/gallium alloy. The alloy is made by mixing aluminum filings into a liquid gallium sample. Purdue researchers demonstrated their method for producing hydrogen by adding water to an alloy of aluminum and gallium. The hydrogen could then be used to run an internal combustion engine. Bruna et al. [6] reported the calculated hyperfine coupling constants (hfcc) and electron-spin g-factors (magnetic moments) of AlGa?. These experimental works trigger us an interest in simulations of gallium aluminum cl
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