Theoretical Investigation of the structures and stability of gas phase neutral and cationic TixOy clusters.

Abstract

By Baljeet Kaur, M.S. A thesis submitted in partial fulfillment of the requirements of the degree of Master of Science at Virginia Commonwealth University. Virginia Commonwealth University, 2010. Major Director: Shiv N. Khanna, Professor, Department of Physics Theoretical investigation of the structure and stability of neutral and cationic TixOy cluster series (where y =2x-1, 2x, 2x+1) have been performed. The lowest lying structures for the neutral clusters are usually found in the singlet state. Generally, in bulk and in the case of the neutral TixOy clusters, the 2x cluster series is relatively more abundant than the 2x-1 and the 2x+1 cluster series. But in the case of cationic TixOy clusters, the 2x-1 series is more abundant. To understand the origin of the stability of the TixO2x-1 + clusters, we use density functional theory within the NRLMOL set of codes. Different analyzing factors such as ionization potential, TiO2 removal energy, oxygen removal energy, binding energy per atom and HOMO-LUMO gap have been used to examine the relative stability of TixO2x-1 + clusters. After analyzing the above criteria, we find that the ionization potential and HOMOLUMO gap are more reliable, as the low ionization potential of the 2x-1 series generally implies low HOMO-LUMO gap and suggests that the 2x-1 cluster series more likely prefer to remain as cations. To further confirm this, we examine the density of states of Ti3O5 and Ti3O6 which show a larger HOMOHOMO-1 gap in case of Ti3O5, indicating that the cluster would like to lose an electron for enhancing electronic stability.