【作者】 庄琼云；

【导师】 朱梓忠；

【作者基本信息】 厦门大学 ， 凝聚态物理， 2009， 硕士

【摘要】 金属团簇是团簇家族中的重要成员,在理论和实验方面都得到了广泛的研究。小的金属团簇通常能够表现出净磁矩,对于金属团簇的电子结构和磁性的研究可以更好的理解金属团簇的物理和化学特性。密度泛涵理论的发展就为物质的电子结构性质的理论研究打开了一个广阔的天地,提供了关键的方法步骤。本论文中采用了基于自旋极化的密度泛函理论的第一原理方法,对简单金属小团簇Al_n（n=2-7）的磁性,重金属小团簇W_n（n=2-7）磁性,Al₄团簇在NaCl（001）表面的结构和磁性进行了计算,主要内容包括:1)对简单金属铝的小团簇Al_n（n=2-7）的结构特性和磁性进行了理论计算。结果表明:团簇的结合能随着团簇中原子数的增加而增大;虽然Al是简单金属,但是其小团簇Al_n（n=2-7）具有磁性,磁矩在1μ_B和2μ_B间变化;通过能级图分析了Al_n团簇磁矩的变化规律。此外,还分析了Al_n团簇的磁矩,结合能,能量的一阶和二阶差分随原子数n的变化,讨论了最稳定团簇Al₅的电子结构和电荷密度。2)对重金属钨的小团簇W_n（n=2-7）的结构特性和磁性进行了理论计算。结果表明:团簇的结合能随着团簇中原子数的增加而增大;虽然W的体材料不具有磁性,但是W的一些小团簇可以表现出磁性,如W₃、W₄和W₇,其磁矩均为2μB;通过能级图我们分析了W_n团簇磁矩的变化情况。此外,还分析了W_n团簇的磁矩,结合能,能量的一阶和二阶差分随原子数n的变化,讨论了最稳定簇W₄的电子结构和电荷密度。3)对Al₄团簇在NaCl（001）表面的结构和磁性进行计算。我们计算了Al₄团簇的重心吸附在NaCl表面上两种桥位,两种空位,在Na原子的顶位以及在Cl原子的顶位的结构、平均每个Al原子的吸附能、最低的Al原子和NaCl（001）表面原子之间的距离和磁矩。计算结果表明:Al₄团簇的重心吸附在NaCl表面上Na的项位是最稳定的结构,吸附能最大,总能最大,最低的Al原子和NaCl（001）表面原子之间的距离最小,但是团簇的磁矩为零;而在其他位置Al₄团簇保留了团簇在自由空间的磁矩。更多还原

【Abstract】 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.更多还原