Structural, Electronic And Magnetic Properties Of CoPt Alloy Clusters:the Density Functional Theory Investigation

The nanoclusters, being the lowest dimension of material, can not only present novel physiochemical properties that nanomaterials often exhibit, but also be acted as the building-unit to construct large nanostructures. Since the concept of cluster was firstly putted forward forty years ago, the nanoclusters come into being the ideal systems in the research fields of condensed matter physics, materials physics, chemistry and chemical engineering. Although mono-elemental clusters have been comprehensively studied, the investigation on bimetal clusters is embarrassed by their atomic component and complex structures. The additional freedom of bimetal clusters benefit their advantages with adjustive physical properties, meeting the functional requirement of clusters. In addition, the interactions between different elemental atoms would induce some novel characters that mono-elemental clusters do not have. With the rapid developments of computational method and the level of computer hardware in recent years, it is possible to perform the investigations on bimetal clusters. In bimetallic clusters, special focus is intensively concerned on CoPt clusters, due to their two distinctive properties:good catalysis and advantage magnetic properties.The density functional theory (DFT) based generalized gradient approximation (GGA), together with the all electron potential method, has been employed to investigate the geometrical evolution, cluster stability, electronic structure, and magnetic property of CoPt bimetallic clusters. To localize the minimum of energy surface, abound possible structures that are the lowest energy structure of other bimetallic clusters, as well as the initial structures that are designed in terms of bonding tendencies of Co and Pt atoms, are optimized to confirm the ground state strucutrues. By analyzing the results, the geometrical evolution, electronic structure, and magnetic property of bimetallic CoPt clusters (n=1-13,38,55) have been obtained. The results are followings:Con-xPtx bimetallic clusters usually exhibit the geometrical structures of the corrsponding pure Co clusters, but tend to form the segregation effect in cluster (Pt atoms prefer to occupy the surface position but Co atoms are apt to be inside of the structure). The cluster stabilities increase with the increasing of cluster size or the decreasing of Pt concentration, and the increasing stability is originated from the competitions between bond-lengths and coordination numbers. Monoatomic doping can slightly enhance the stability of CoPt clusters but the increasing magnitude would decrease weakly with the increasing Pt compoment. The HOMO-LUMO gaps change irregularly along with the size and concentration, indicating that the stability of cluster is weakly contributed from the electronic closure eflfect. The Co and Pt atoms always maintain the ferromagnetic coupling in CoPt cluster. The doping Pt atoms always reduce the total magnetic moment of clusters, but induce additional moments on Co atoms to enhance the local polarization of Co atoms. The Cocore-Ptshell configuration of CoPt clusters and its superior magnetic properties make them advantage to develope new high density storge material.