The structural and electronic properties of () clusters
Introduction
Small clusters have been investigated in recent years with an increasing interest due to their potential applications in industry. Many experimental and theoretical studies show that wonderful physical and chemical properties of the clusters are greatly determined by their structural properties, such as size, shape, and composition. Bimetallic clusters or alloys of these metals are of special interest due to their optical properties [1], [2]. Metal nanocrystals of different shapes and sizes have been reported experimentally [3]. Recently Rao et al. reported the structural effect on electronic properties of Au–Cu binary clusters [4]. And De and Rao presented the SPR absorption for pure metal and alloy clusters by embedding Au–Cu nano alloys in film [2]. To our knowledge, however, there have been no theoretical reports on electronic properties on Cu–Ag binary yet. Here in this work, we report our DFT studies on clusters with a fixed size of while varying the composition of the cluster from pure Cu () to pure Ag () through ().
Section snippets
Computational methods
The calculations were carried out using Amsterdam density functional (ADF) code [5]. The zero-order regular approximation (ZORA) was adopted in all the calculations to account for the scalar relativistic effect [6]. For geometry optimizations, the generalized gradient approximation (GGA) with density gradient corrections of Perdew and Wang (PW91) was employed [7]. The standard Slater-type-orbital (STO) basis sets with quality of triple-zeta plus polarization functions (TZ2P) were used. For
Results and discussions
Fig. 1 shows the optimized structures of the clusters along the composition of the bimetallic clusters (), which are classified as triangular shape (A), capped shape (B) and W-shaped (C). There are seven possible combinations in each shape ranging from pure to with the cluster formula as (). Fig. 2 displays the value of binding energies which are calculated aswhere , and are the total energies of one Cu atom,
Summary
In this work, we study () clusters through the theoretical characterization of their molecular structures, binding energies, electronic properties and absorption spectra using density functional theory in all-electron calculations. The triangular shape (A) clusters and capped shape (B) clusters are usually stabler than W-shaped (C) clusters. It is demonstrated that the HOMO–LUMO gaps vary inversely to the average bond length. The analysis of absorption spectra of ()
Acknowledgments
This work was supported by the National Science Foundation of China under Grant No. 10774148, the special Funds for Major State Basic Research Project of China (973) under Grant No. 141J00775601, Knowledge Innovation Program of Chinese Academy of Sciences, and Director Grants of CASHIPS. Part of the calculations were performed in Center for Computational Science of CASHIPS and the Shanghai Supercomputer Center.
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