First-Principles Studies of Ionic and Transition Metal Microclusters.

In this dissertation two different kinds of clusters, ionic and transition-metal clusters, have been investigated by using a first-principles, all-electron, linear combination of Gaussian orbital method. In ionic clusters, the nature of excess electron states in different alkali-halide clusters is presented. The possibility of the spontaneous localization -induced dissociation of the cubic (Na)_ {14}(Cl)_{13} cluster has been addressed and the alternate mechanism of dissociation of the neutral cluster is proposed. The magnetic and structural ordering in iron and nickel clusters have been studied. The ground states of iron and nickel clusters are all ferromagnetic with highest dimensional geometry and exhibit a tendency toward enhanced bond length, narrower d-band widths, and maximum pairs of nearest-neighbor bonds. The issue of Fermi level problem in these clusters is also addressed and our solution to this problem is discussed.