Aluminum Clusters Doped Characteristics Of The Study

In this paper, we have investigated the stability and properties of the ground state structures for small Aluminum clusters doped with transition-metal atoms:Zn, Ni and Cu by using Amsterdam Density Functional (ADF) Program. ADF is one of the sophisticated methods based on first principle and it is popular in the research areas of material science. Including general exchange-correlation functional, it provides many advanced XC-energy functional and potential, such as meta-GGA, hybrid exchange-correlation functional, SAOP and GRAC gradient XC-potential. Due to linear scaling and parallel implementations, ADF could calculate the systems with hundreds of thousands of atoms (such as organic compounds with light elements) fast and efficiently.Firstly, we have investigated the structures, stabilities and magnetism of zinc-doped Aln+1 (n=1-9) clusters in detail by using first-principles density functional theory. Our calculated results indicate that the ground state structures of the mixed AlnZn (n=1-9) clusters doped with one zinc atom can be obtained from the most stable structures of the pure Aln+1(n=1-9) clusters by substitutional type. The impurity atom causes local structural distortion due to different atomic radii and different bonding characteristics. It is found that the clusters with total atom number of 3 and 7 exhibit high stability. In addition, the energy gaps Egs between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) show obvious even/odd alternation with cluster size. Furthermore, we investigate the magnetism of the mixed clusters. The Al4Zn, Al6Zn, and Al8Zn clusters with even number of electrons do not have any magnetism. All AlZn, Al5Zn, Al7Zn and Al9Zn clusters have the total magnetic moment of 1.0μB due to one unpaired electron. Unexpectedly, Al2Zn and Al3Zn clusters show respectively total magnetic moments of 2.0 and 3.0μB. The magnetism arises from the sp-d hybridization due to charge transfer and the influence of the impurity zinc atom.Secondly, we have studied AlnNi(n=1-9) clusters, and AlNi,Al2Ni and Al7Ni presented the high stability. Comparing with pure Aln+1(n=1-9) clusters, the impurity atom Ni caused the local distortion. As the cluster size increases, the distortion gradually decreases, but to a certain extent, the symmetry of original structures is destroyed. At the same time, we have investigated the magnetism of the nickel-doped clusters. In the common roles of 3p orbit of Al atoms and 3d orbit of Ni atom, the spin direction of two 3p orbital electrons of Al4Ni cluster parallel upward. Similarly, two electrons of Al6Ni cluster also spin parallel upward. For that reason, the magnetic moment of Al4Ni and Al6Ni clusters are both 2.0μB, and they are magnetic clusters while others are non-magnetic.Thirdly, the equilibrium structures of AlnCu (n=1-9) have been optimized by using ADF program. As a result, compared with other clusters, AlCu and Al7Cu exhibit high stability. But as the symmetry decreases, the dipole moment of impurity clusters are all non-zero. Meanwhile, we also have investigated the magnetism of AlnCu (n=1-9) clusters. The calculation results indicate that after substituting one Al atom by a Cu one, part of charge transferred from Al atoms to Cu atom, and all atoms in the clusters have magnetic moments. Overall, the numbers of electrons of AlCu, Al3CU, Al5Cu, Al7Cu and Al9Cu are even, and all of the electrons are in pairs in molecular orbital, the total magnetic moments are 0.0μB.With odd numbers of electrons, the total magnetic moments of Al2Cu, Al4Cu, Al6Cu and Al8Cu are 1.0μB as one electron is unpaired. Although part of charge has transferred from one atom to another and the magnetic moment of atoms has changed, the total magnetic moment of the clusters is invariable and all of the small aluminum clusters doped with copper atom are non-magnetic.