Structures of small YnAlm clusters (n + m 6 6): A DFT study Natarajan Sathiyamoorthy Venkataramanan a, * , Ambigapathy Suvitha b , Ryunosuke Note b , Yoshiyuki Kawazoe b a Research Center for Compact Chemical Process, National Institute of Advanced Industrial Science and Technology (AIST), 4-2-1, Nigatake, Sendai 983-8551, Japan b Institute of Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan article info Article history: Received 12 December 2008 Received in revised form 13 February 2009 Accepted 16 February 2009 Available online 26 February 2009 Keywords: Bimetallic clusters DFT methods Electronic properties Aluminum clusters Structure and stability abstract We conducted DFT studies on the YnAlm binary clusters of size n + m 6 6, to study electronic property variation, using the PBE1PBE method and Lanl2DZ as basis set. The ground-state geometries of yttrium (n P 4) prefer 3D geometry and Al (m 6 5) desires planar geometry. Yttrium clusters were stabilized by the addition of one or two aluminum atoms. The shape and geometry of the clusters has a profound influence on their band gap and stability. With an increase in the Al composition, segregation was found to occur in the bimetallic systems with the geometry and shape depending on the aluminum composi- tion. The bimetallic clusters have higher electron affinity and stability. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Studies on bimetallic clusters have received great attention owing to their chemical and physical properties, which can be tuned by varying the composition, atomic ordering, and size of the clusters [1]. Their surface structures, compositions, and segre- gation properties are of interest; moreover, these studies have been important in determining chemical reactivity which has led to widespread applications in electronics, engineering and catalysis [2]. Though large advances have been made in experi- mental physics to produce size-selected clusters, they lack the ability to directly explore and assign cluster geometries and dis- criminate between possible isomers. Of particular interest are aluminum alloys which are light weight, high strength, and corro- sion resistance. Hence much research has been carried out to study the bimetallic clusters of aluminum [3–5]. Studies on the substitution of the transition metal show that they increase the stability of the materials. However, theoretical studies of such clusters have faced difficulties due to the presence of d electrons, with complicated electronic ground-states structure with differ- ent spin multiplicities [6]. Yttrium shows great promise as a catalyst [7]. Yttrium in its composites such as Yttrium Aluminum Granite (YAG), finds appli- cations in optical sensors with high sensitivity or in X-ray detec- tion material [8]. Moreover, yttrium can be added to reduce the grain size in chromium, molybdenum, zirconium, and titanium, and to increase the strength of aluminum and magnesium alloys [9]. Besides, yttrium alloys are extensively used in bulk metallic glasses [10]. Aluminum and its alloy clusters were found be capa- ble of acting as reversible hydrogen storage materials [11]. Only recently, attention has been paid to the structure and stability of monometallic yttrium clusters by using the DFT method [12,13]. In a recent study, Yuan et al. reported on the structure and electronic properties of small yttrium clusters of size n = 2– 17 and observed that the growth evaluation favors 3D clusters formation with a oscillatory behavior in their HOMO–LUMO gap. On the contrary, much attention was paid to ab initio and density functional modeling of aluminum clusters [14–18]. Ahl- richs and Elliot investigated the structure stability of aluminum clusters and observed that the 2D planar configurations were of the lowest energy for clusters of m = 5. The nature of the hetero- metallic bond has been extensively studied using experimental and theoretical methods [19,20]. Theoretical investigations have been done on CuAl  clusters [21], Al–Ti clusters [3], Al–Ni clus- ters [4], Al–B clusters [22], Al–Si clusters [5], and Al–Fe clusters [23]. With the view to understanding the structure, stability and properties, of the type YnAlm (m + n 6 6), we have made a theoret- ical investigation on the small bimetallic clusters over the com- plete composition range from pure yttrium to pure aluminum cluster. We present the results obtained for various YAl clusters according to the composition of the clusters and have compared their properties with monometallic clusters. 0166-1280/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2009.02.017 * Corresponding author. Tel.: +81 22 237 5214; fax: +81 22 237 5215. E-mail addresses: nsvenkataramanan@gmail.com, ns-venkataramanan@aist. go.jp (N.S. Venkataramanan). Journal of Molecular Structure: THEOCHEM 902 (2009) 72–78 Contents lists available at ScienceDirect Journal of Molecular Structure: THEOCHEM journal homepage: www.elsevier.com/locate/theochem