Co_13-xMn_x（x=1-12） Bimetallic Clusters And Endohedral Si₂₀ Fullerene-like Cage: A DFT Investigation

During the past thirty years, much interest has been paid to the study about structures andproperties of atomic clusters, originating from their many fascinating physicochemicalproperties which are quite different from the bulk state. Magnetic transition metal (TM)clusters possess great potential applications in many fields, such as high-density magnetismrecording, catalysis, optics, and biomedical aspects. There has been great attention inmagnetic properties of the binary alloy clusters composed of cobalt and manganese which arethe3d transition metal representative. Besides, along with the deep understanding of peculiarstructures and property of carbon fullerence, people also have great interest in the stability ofsilicon fullerence. Due to the lack of sp2hybridization of silicon bond, pure silicon cage cannot be stable；Research shows that the application through encapsulated the central atom insilicon cage is more available than carbon fullerence.Basing on the frame of density functional theory (DFT), we research the evolution of thesize, the stability of the structure, electronic properties, and magnetic of Co13-xMnx(x=1-12)clusters using the generalized gradient approximation (GGA) with the PBE; we stillcalculated the structure and stability of two3d transition-metal atoms(TM2) doped Si20clusters with DFT-GGA/PBE, which composed TM2@Si20clusters, and further discussedthe effect of TM2in silicon fullerence. Relevant conclusions are summarized as follows:The ground state geometric structures of Co13-xMnx(x=1-12, x represents the number ofMn atoms) clusters prefer icosahedral configurations with high symmetry. In doped Co13-xMnxclusters, cobalt atoms prefer to occupy surface positions expect Co9Mn4, Co5Mn8, Co7Mn6clusters which a cobalt atom occupy the central position of the clusters, whereas Manganeseatoms prefer to occupy central position of the clusters.With the number of Mn atoms increased, the binding energy of Co13-xMnxclustersgradually decreased, this indicate that the stability of the clusters decreased. The second orderdifference of the binding energy display three peaks when x=3,5,8. Compared with theresults from clusters binding energy we find that Co10Mn3, Co8Mn5and Co5Mn8clusters aremore stable, they are magic number clusters. Co5Mn8cluster has the most stable chemicalproperty among them. In the process of forming doped clusters, Co atoms can get electron more easily than Mn atoms. When x≤3, the total magnetic moment of the Co13-xMnxcluster increased with the increase of x. When x≥9, the total magnetic moment of theCo13-xMnxclusters increased with the decrease of x. The total magnetic moment of theCo13-xMnxcluster show odd-even oscillation behaviors when3<x<9. When x is eight, theHOMO-LUMO gap is a maximum, the total magnetic moment of the cluster also getmaximum. We infer that Co5Mn8can lay the foundation of good stable magnetic materials.In TM2@Si20(TM=Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn) doped clusters, in addition to Fedimers doped Si20with a Fe atom outside the cage of Si20, the other dimers in3d transitionmetal doped Si20are all located inside the cage. The ground state of Ti2, V2, Co2and Ni2doped Si20have the higher binding energy which can be more stable. Doping transition metalcan make the cage of Si20contracted, the Si20cage of Mn2@Si20is minimal among dopedclusters. Ti2@Si20has the maximum Embedding energy which make the Si20cage more stablethan the other doped clusters. Sc2@Si20has the maximum HOMO-LUMO gap and the moststable chemical property. In TM2@Si20doped clusters, all dimers show electronegative, thetransfer of charge present inverted phenomenon. The transition metal which have smallerelectronegativity are able to get the charge of silicon and be charge receptors.Along with3d transition metal atoms encapsulated in Si20cages, their spin magneticmoment have been changed. The manganese atom has a large spin moment about1.405μB,while the spin moments of Cr, Co, Ni, Cu, and Zn are entirely quenched upon doping into theSi20.