First-principles Study Of The Adsorption Of H₂ Molecule On Zirconium Clusters And Zr_nCr Clusters

In this thesis, employing first-principles quantum chemistry methods based on Density-Functional Theory (DFT), we study the adsorption of H₂ molecule on zirconium clusters; the geometric structures, magnetic properties and electronic properties of zirconium clusters doped with transition metal Cr. The main contents are presented as the followings:We have systematically studied the growth behavior of small zirconium clusters of up to 15 atoms and the adsorption of a H2 molecule on the minimum energy clusters using the density functional theory (DFT) within the generalized gradient approximation (GGA) as implented in DMOL³. The calculated results show that from n=4, the low-energy clusters grow three dimensionally and prefer to form compact structures. By the analysis of the fragmentation energy and the second-order difference of binding energy, we find that Zr₇, Zr₁₃ and Zr₁5 clusters are more stable than theirs neighbours. H2 prefers a dissociative chemisorption on the zirconium clusters. The chemisorption energies of Zr₄ and Zr₁₃ clusters are found to be the highest and the second highest, but the chemisorption energies of Zr₇ cluster is the lowest. This shows that both Zr₄ and Zr₁₃ clusters are of high activity with respect to the H2 chemisorption, while the Zr₇ cluster is of high inertness.We choose the Cr atom as impurity and study the equilibrium geometries, electronic and magnetic properties of Zr_nCr (n=2-14) clusters using the density functional theory (DFT) within the generalized gradient approximation (GGA). The calculated results show that the Cr atom remains on the surface of clusters for n<8, and then slowly getting trapped beyond n= 8. For Zr₁₂Cr, we obtain an icosahedral structure (Ih) with the Cr atom in the cage center. Moreover, Zr₁₂Cr is more stable and less reactive because of its highest the HOMO-LUMO gap and global chemical hardness. We also discusse the magnetic properties of the Zr_nCr clusters.The magnetic moment of the Cr atom and the Zr_nCr clusters is completely quenched from n=9. According to the Mulliken charge population, the internal electron transfer in Cr atom and the charge transfer between Cr and Zr atoms should be major reasons for the changes of the magnetic moment of the Zr_nCr clusters and the Cr atom.