Ab Initio Calculations On The Magnetism Of Small-sized Metal Clusters

Metal clusters are important members of the cluster family,and many theoretical and experimental studies have been carried out on their properties.Small metal cluster usually shows magnetism.The study of the electronic structures and magnetism of metal clusters could help us understand the physical and chemical properties of metal clusters better.The development of density functional theory(DFT) has an opened a wide realm for the studies of electronic structures,and provided a pivotal scheme.In this dissertation,by employing the first-principles calculations based on the spin-polarized density functional theory,the structural properties and magnetism of Al_n(n = 2-7),W_n(n = 2-7) small clusters and Al₄ clusters on the NaCl(001) surface have been studied.The main results are as following:1) The structural properties and magnetism of Al_n(n = 2-7) small clusters have been studied.The calculations show that:the binding energies increase with the number of atoms in the Al_n cluster;the small-sized Al_n(n = 2-7) clusters can exhibit magnetism though Al is a simple metal,with the magnetic moments change between 1μ_B and 2μ_B.From the plot of energy levels,the magnetic moments of spin-polarized Al_n clusters are discussed.Furthermore,the magnetic moment,the binding energy,the first and second differences of binding energies versus the number of atoms in the clusters are analyzed.The electronic structure and charge density of the most stable cluster Al₅ are also discussed.2) The structural properties and magnetism of W_n(n = 2-7) small clusters have been studied.The calculations show that:the binding energies increase again with the number of atoms in the cluster;although the bulk tungsten does not show magnetism, some of the small-sized W_n clusters can exhibit magnetism,i.e.,when n equals to 3,4 and 7,all with a magnetic moment of 2μ_B.From the plot of energy levels,the magnetic moments of the spin-polarized W_n clusters are discussed.Furthermore,the magnetic moment,the binding energy,the first and second differences of binding energies versus the number of atoms in the cluster are analyzed.The electronic structures and charge density plots of the most stable cluster W₄ are also discussed.3) The structural properties and magnetism of Al₄ cluster on the NaCl(001) surface have been studied.We calculated the structures,the binding energy,the distance between the lowest Al atoms and the NaCl(001) surface as well as the magnetic moment of the Al₄ clusters on the NaCl(001) surface.The adsorption sites considered are two kinds of bridge sites and hollow sites,the top site of the Na atom as well as the top site of the Cl atom.The results show that Al₄ clusters on the top site of the Na atom is the most stable structure,with the largest binding energy and the smallest distance between the lowest Al atoms and the NaCl(001) surface,however, its magnetic moment is zero.On the other hand,adsorption sites except for the top site of the Na atom can retain the magnetic moments of Al₄ cluster in the free space.