Influence of Sn interaction on the structural evolution of Au clusters: A first principles study Suman Kalyan Sahoo a , Sandeep Nigam b , Pranab Sarkar a , Chiranjib Majumder b,⇑ a Dept. of Chemistry, Visva-Bharati, Santiniketan 731 235, India b Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India article info Article history: Received 4 May 2012 In final form 25 June 2012 Available online 1 July 2012 abstract Here we report the structural and electronic properties of Au n Sn (n = 2–13) clusters by using pseudo- potential and LCAO–MO method. A comparison between the structures of Au n and Au n Sn clusters reveals that while Au n clusters favor planar isomers up to n = 13, Au n Sn clusters follow a different trend; 3D structure for n = 3 and 4, quasi planar in the size range n = 5–11, and again 3D isomers from n = 12 onwards. Enhanced contribution of Au p-orbital and significant charge transfer from Sn to the gold atoms is attributed for such interesting growth pattern of Au n Sn clusters. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction The structure and stability of small metal clusters are of great interest. The size-dependent properties of metal clusters strongly depend on the atomic arrangement and consequently, on their electronic structure [1]. In recent years, an extensive research has been carried out on gold clusters, mainly due to their wide use in the catalysis, microelectronics and optical materials [2–42]. Small gold clusters show unique behavior in terms of their ground state geometries. In particular, it is interesting to note that gold clusters remain planar even beyond n = 6. Moreover, it is observed that the equilibrium geometries of charged gold clusters are often different from the corresponding neutral cluster [19–26]. Doping of an impurity atom in pure clusters has been used to underscore the variation of properties as a function of cluster size and to tune the chemical reactivity of the host system more pre- cisely [27–36]. Small clusters are agglomeration of few atoms, and therefore, an impurity atom corresponds to extremely high dopant concentration and affects the physico–chemical properties significantly [2–5]. Wang and co-workers [29] reported that iso- electronic substitution of Au atom by Cu or Ag shifts the onset of 2D–3D structural transition to a smaller size. Yuan et al. [30] stud- ied the Ni, Pd, Pt doped Au clusters and found that for Ni, the host cluster geometry does not change, but for Pd and Pt doped Au clus- ters, the ground state geometries changes significantly. Dong et al. [31–33] studied the Sc, V, Mn and Fe doped gold clusters and con- cluded that, the ground state geometries of doped clusters favors planar configuration with transition atom occupying the higher co-ordination site. Li and co-workers [34] reported that the most stable isomers of Au n Zn (n = 2–10) clusters favor planar structures, which resembles with pure gold cluster anions. Based on all- electron scalar relativistic calculation Kuang et al. [35] reported that the most stable isomers of Au n Pt (n = 1–12) clusters are distorted slightly in comparison to pure gold Au n+1 clusters, but still retains the planar motifs due to the strong scalar relativistic effect. Although a large number of studies are available on transition- metal doped gold clusters [3,5,27–36], few are available using non transition elements as dopants. One of the major differences is the preference of non-planar geometries using S or P block elements as dopants. Heiz et al. [37] reported that Na doping in gold clusters leads to higher polarization and more directionality of the metal– metal bonds. Previously we have reported the ground state geom- etries of Au clusters doped with various P block elements [38–41]. For Si doped Au clusters, an early onset of non-planar geometries of Au n Si clusters (n = 3) has been observed, which is strikingly differ- ent than what is reported for transition-metal doped Au clusters. The reason for the preference of non-planar geometry of Au n Si clusters was attributed to the involvement of p-orbital electrons into the bonding, which results in a strong directional covalent bond. Recently Wang and co-workers [42] have carried out a com- bined photoelectron spectroscopy and computational study on the structural evolution of doped gold anion clusters MAu n À (M@Si, Ge, Sn; n = 5–8). It was found that for n = 6 and 7, all three doped clus- ters MAu n À (M@Si, Ge, Sn) exhibit similar quasi–planar structures. Importantly, they proposed that 2D–3D transition for Si doped clusters occurs at n = 8, and in contrast Ge and Sn doped clusters have quasi–planar structure. To the best of our knowledge, so far there is no theoretical study on neutral gold–tin bimetallic clusters. In general, there is a funda- mental difference between Si and Sn interactions. In bulk, Si is a semiconductor and has stronger tendency to form covalent bonds. 0009-2614/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cplett.2012.06.055 ⇑ Corresponding author. E-mail addresses: chimaju@barc.gov.in, chimaju@magnum.barc.ernet.in (C. Majumder). Chemical Physics Letters 543 (2012) 121–126 Contents lists available at SciVerse ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett