Dynamics and electronic structure of neutral and multiply charged metal clusters using density functional theory (Calcium, Rhodium).

摘要

Density functional theory (DFT) stands as a powerful tool for evaluating properties of atomic clusters. On the other hand, more investigations of heavy metal clusters are needed to understand the basic binding processes. Hence, the first part of my dissertation concentrates on the study of the magnetic and electronic properties of small rhodium clusters with two different exchange-correlation functionals. Local (LDA) and non-local (GGA) schemes are applied to yield the accurate binding energies, equilibrium geometries, vibrational frequencies, and magnetic moments. Ground states of small rhodium clusters were found to display interesting magnetic properties. From these studies I find that the ground state of Rh₂ is confirmed to be a quintuplet state, trigonal Rh₃ is predicted to be a sextuplet, Rh₄ in its tetrahedral configuration is a singlet, Rh₅ in a sextuplet state is a square pyramid, and Rh₆ is a sextuplet state in the octahedron configuration.; Determination of properties of large heavy metal clusters requires extremely high computational power. As the size of clusters increases, the use of density functional theory becomes impractical from the computational point of view. Therefore, the second part of this dissertation deals with the development of a model many-body potential for estimating structural properties of rhodium clusters with moderate computational effort. Based on simulation data collected from first-principles calculations, a new many-body potential is proposed where the parameters are size dependent and fitted on the energy surfaces of Rh₂ through Rh₆ clusters. Using this potential the energetically most stable paramagnetic and ferromagnetic structures are generated up to Rh₅₆. The melting temperature. calculated as a function of cluster size, displays a monotonic trend towards the bulk limit. Large size simulations, up to sizes of 400, suggest that the growth follows a route close to the face-centered cubic (fcc) symmetry.; With advanced computational power and innovating facilities, theoretical predictions and experimental measurements could supplement themselves. Therefore, the final part of this dissertation concentrates on the study of multi-channel fragmentation of doubly charged calcium clusters up to the cluster size of the octamer. The preferred fragmentation channels were determined. and I show that fission channels for sizes as large as the heptamer are preferred in the fragmentation process. Very small clusters up to $Ca++4$ are linear. $Ca++8$ needs less energy to evaporate than to fission, this is the “critical size”. All my findings support the experimental results of Martin's group [49].