The structural and electronic properties of ${\mathrm{Cu}}_m{\mathrm{Ag}}_n$ ($m+n=6$) clusters

Abstract

The structural and electronic properties of ${\mathrm{Cu}}_m{\mathrm{Ag}}_n$ ($m+n=6$) clusters have been investigated through density functional theory. Our results show that the triangular shape (A) clusters and capped shape (B) clusters are generally stabler than W-shaped (C) clusters. It is shown that the HOMO (highest occupied molecular orbital)–LUMO (lowest unoccupied molecular orbital) gaps vary inversely to the average bond length. We also investigated spectra of ${\mathrm{Cu}}_m{\mathrm{Ag}}_n$ ($m+n=6$) clusters, which shows that the dominant peaks near 3.5 eV are contributed from the electrons of $\mathrm{Cu}3d$, $\mathrm{Cu}4s$ and $\mathrm{Ag}5s$.

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 ${\mathrm{SiO}}_2$ 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 $n=6$ while varying the composition of the cluster from pure Cu (${\mathrm{Cu}}_6$) to pure Ag (${\mathrm{Ag}}_6$) through ${\mathrm{Cu}}_m{\mathrm{Ag}}_n$ ($m+n=6$).