Study of metal clusters using quantum mechanics methods

Recently, nanometer-sized systems and structures have been a topic of great interest for experimental and theoretical investigations. While many researchers in this field use a variety of techniques and materials to create and study such systems, most share a common element: some kind of cluster or quantum dot. A cluster is a group of atoms that come together by self-assembly. They can be comprised of anywhere between 2 and ~10000 particles and represent a sort of bridge between the atomic and bulk size regimes. Much of the interest in clusters is fuelled by the many possible applications of clusters and the related nanoscale technologies. Nano clusters not only exhibit interesting electronic and optical properties intrinsically associated with their low dimensionality and the quantum confinement effect, but also represent the critical components in the potential nanoscale electronic and photonic device applications. The role of clusters in chemical systems is also intriguing. As particle size decreases, the ratio of surface atoms to interior atoms increases. Cluster materials are chemically more reactive than bulk materials. Theoretically, these metal clusters may be categorized according to the level of difficulties encountered in their computational treatment. In this sense, alkali-metal clusters proved particularly useful because they could be easily characterized experimentally and investigated with less computational effort compared to the other metal clusters. Hence, they have been widely studied both theoretically and experimentally.Experimentally, metal clusters have been studied using electronic-spin-resonance (ESR), abundance spectrum, photoelectron spectroscopy (PES), Knudsen effusion and X-ray photoelectron spectroscopy (XPS), etc. At the same time, various theoretical approaches have also been used to investigate the clusters, such as embedded-atom-method (EAM), pair-potential theory, semiempirical n-body potential theory, molecular dynamics (MD) method , pseudopotential local spin density (LSD) approximation and the first-principles (FP), etc. In all of these theoretical methods, the FP is the most precise one. Magnesium is an element that exhibits a transition from weak van deer Waals bonding in the diatomic molecule to metallic bonding in the bulk. Thus, many experimental techniques and theoretical simulations have been used to investigate the geometrical structure, electronic properties and bonding nature of Mg clusters. From the theoretical point of view, Reuse et al. explored structural and electronic properties of neutral and charged magnesium clusters (n=2-7) using the LSD approximation. Using the density-functional MD method, Kumar and Car calculated the gap between the highest-occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO–LUMO gap) for neutral magnesium clusters over the size range from 2 to 11 and the jellium-type magic clusters were observed. Lyalin et al. investigated evolution of the optimized structures and electronic properties of neutral magnesium clusters with increase in cluster size.