Physics Letters A 374 (2010) 4133–4139 Contents lists available at ScienceDirect Physics Letters A www.elsevier.com/locate/pla Structure, electronic and magnetic properties of Cr-doped (ZnS) 12 clusters: A first-principles study Hongxia Chen a,b , Daning Shi b,∗ , Jingshan Qi b , Baolin Wang b,c a College of Physical Science and Electronic Techniques, Yancheng Teachers University, Yancheng 224002, China b Department of Physics, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China c Department of Physics, Nanjing University, Nanjing 210093, China article info abstract Article history: Received 2 June 2010 Received in revised form 11 August 2010 Accepted 11 August 2010 Available online 17 August 2010 Communicated by R. Wu Keywords: Diluted magnetic semiconductor Clusters Density functional theory We have studied the structural, electronic, and magnetic properties of (ZnS) 12 clusters doped with one (monodoped) and two (bidoped) Cr atoms in terms of a first-principles method. Substitutional, exohedral, and endohedral doping are considered. The substitutional isomer is found to be most favorable in energy for monodoped clusters, while the exohedral isomers are found to be most favorable for bidoped clusters. The magnetic coupling between the Cr atoms is mainly governed by the competition between direct Cr–Cr antiferromagnetic (AFM) interaction and the ferromagnetic (FM) interaction between two Cr atoms via S atom due to strong p–d hybridization. Finally, we show that the exohedral bidoped (ZnS) 12 clusters favor the FM state, which has potential applications in nanoscale quantum devices.  2010 Elsevier B.V. All rights reserved. 1. Introduction The discovery of ferromagnetism in Mn-doped GaAs with a Curie temperature of 110 K has created an intense interest in the study of dilute magnetic semiconductors (DMS) [1]. Studies of these systems are driven not only by the academic interest in un- derstanding the origin of ferromagnetism but also by the potential applications. In an effort to raise Curie temperature to values above room temperature, whence DMS could become commercially visi- ble, there has been a push towards hosts with wide band gap such as Zinc sulfide (ZnS, 3.7 eV at 300 K) [2,3]. Moreover, compared with bulk and film, cluster usually displays some unique prop- erties due to its special geometry and the quantum confinement effect, which hold promise for advanced nanodevice applications [4–6]. With the recent emergence of nanoscience and nanotech- nology, doping of clusters and nanoparticles has also attracted a great deal of attention because of their prospects in technological applications [7–10]. The pristine ZnS clusters have been extensively studied both experimentally [11–13] and theoretically [14–20]. In contrast, the doped ZnS clusters, especially those doped with transition metal (TM) elements, are less to be investigated. The effect of impurity doping on the structural stability and magnetism of the cluster is not well understood yet. Moreover, among these cage-like ZnS structures, the (ZnS) 12 is the smallest cage structure with the high- * Corresponding author. Fax: +86 25 52113807. E-mail address: shi@nuaa.edu.cn (D. Shi). est possible symmetry (octahedral) [21], which can be taken as a good candidate for the investigation of Cr-doped ZnS clusters. Previous works have been performed on the (ZnO) 12 , (GaAs) 12 , (ZnTe) 12 , and (CdS) 12 clusters doped with TM atoms [22–25]. For instance, Liu et al. have investigated the structure, electronic, and magnetic properties of Mn-doped (ZnO) 12 clusters and concluded that Mn impurities have a tendency of clustering and the coupling is dominated by short-range AFM ordering [22]. Also, Yadav et al. [24] and Ghost et al. [25] have found that both the short-ranged FM and AFM coupling could exist in the Cr-doped (ZnTe) 12 and (CdS) 12 clusters, respectively, depending on the Cr–Cr distance and the local environment of Cr atoms. In this Letter, we present a systematical theoretical investi- gation on the geometry, electronic, and magnetic properties of (ZnS) 12 clusters doped with one or two Cr atoms. For the five opti- mized isomers of the monodoped case, the doping-induced struc- tural changes of the clusters are very small. For the bidoped case, most importantly, we show that the exohedral bidoped (ZnS) 12 clusters favor the FM state, which has potential applications in nanoscale quantum devices. 2. Theoretical method and computational details The calculations are performed using spin-polarized density functional theory (DFT), as implemented in the DMOL pack- age [26]. This method can perform accurate and efficient self- consistent calculations using a rapidly convergent three-dimen- sional numerical integration scheme. All electrons treatment and double numerical basis set including d-polarization functions (DND) 0375-9601/$ – see front matter  2010 Elsevier B.V. All rights reserved. doi:10.1016/j.physleta.2010.08.030