| Atomic clusters had attracted lots of interests in the last three decades. The considerable interest in this field is brought about by two major expectations. First, atomic clusters form a bridge between molecular physics and condensed matter physics; secondly, materials synthesized by assembling the most stable clusters may be technologically important. Unfortunately, there is no experimental technique that can provide direct information on cluster geometry. The only method that enables determination of cluster geometries at present is, thus, based on theoretical calculations. In this thesis Density functional theory with generalized gradient approximation for the exchange-correlation potential has been used to calculate the global equilibrium geometries and electronic structure of neutral, cationic, and anionic aluminum clusters containing up to 13 aluminum atoms. The total energies of these clusters are then used to study the evolution of their binding energy ,relative stability, and ionization potential as a function of cluster size. I also calculate the HOMO-LUMO Gap to determine the cluster's relative salability. In this thesis, I found several new equilibrium geometries, such as: Al6 , Al6+ , Al6- , Al7- , Al9 , Al9+ , Al9- , Al10- and Al11- . The geometries are found to undergo a structural change from two dimensional to three dimensional when the cluster contains 6 atoms. The binding energy evolves monotonically with size. Although the neutral clusters do not conform to the jellium model, the enhanced stability of these charged clusters, such as: Al7+ , Al7- , Al11- and Al13- , is demonstrated to be due to the electronic shell closure. The calculated results agree very well with available experimental data on ionization potentials. The unusual stability of Al7 in neutral, cationic, and anionic form compared to its neighboring clusters is argued to be due to its likely existence in a mixed valence state. This also agrees with current experiment results.
|
PDF Full Text Request