First Principles Study Of The Ground-state Structures Stability As Well As Magnetism Of Zr_n, Zr_nFe Clusters

Clusters play an important role in understanding the transition from the microscopic structure to macroscopic structure of matter. The research field of clusters, particularly microclusters, has shown a rapid development in both experimental and theoretical investigations in the last two decades. Although there has been considerable improvement in the experimental techniques, there are still difficulties in the production and also in the investigation of isolated microclusters of some elements.Computer simulations provide help for the understanding of the experimental observations on the one hand, and they can also be applied for systems in which experimental data are practically difficult to obtain on the other hand. Atomistic level computer simulations using first-principles have been used successfully to investigate bulk, surface, and cluster properties of elements.In this thesis,we have studied the geometric structure,stability,as well as magnetism of Zrn(n=2-16)clusters and ZrnFe(n=2-13)clusters by using the density functional theory.Chapter one introduces the cluster science and its research meaning as well as the review of the studies having done on clusters.In chapter two, the geometries,total energies,and frequencies of Zrn(n=2-16)clusters have been systematically investigated by using density functional theory with the generalized gradient approximation,the equilibrium geometries at different spin multiplicities as well as the ground-state structures have been determined.The calculated results on the averaged binding energy, fragmentation energy ,the second-order difference of clusters energies as well as the HOMO-LUMO gap of the Zrn(n=2-16)clusters indicate that the relative stabilities of Zr2,Zr5,Zr7,Zr13,Zr15 are stronger than other sized clusters. The true ground state for Zr13 cluster is icosahedral structure with Ih symmetry,moreover the stability of Zr13 is strongest among all the investigated clusters.In chapter three,the geometries,total energies,and frequencies of ZrnFe(n=2-13)clusters have been systematically investigated by using density functional theory with the generalized gradient approximation,the equilibrium geometries at different spin multiplicities as well as the ground-state structures have been determined.The calculated results on the averaged binding energy,the second-order difference of clusters energies as well as the HOMO-LUMO gap of the ZrnFe(n=2-13) clusters indicate that the relative stabilities of Zr5Fe,Zr7Fe,Zr12Fe are stronger than other sized clusters.The true ground state for Zr12Fe cluster is icosahedral structure with Ih symmetry,moreover the stability of Zr12Fe is strongest among all the investigated clusters.In addition,not only the relative stabilities of Zr5Fe,Zr7Fe as well as Zr12Fe clusters are stronger than other sized clusters but also they are all magnetic clusters (however,the magnetic moment of Zrn clusters is quenched for n≥5),thus it can be seen thant we can acquire magnetic clusters with higher stabilities by choosing appropriate doping atom.Mulliken population analysis shows that there is weak charge transfer from Zr atoms to Fe atom except for Zr12Fe cluster in which small amount charge transfers from Fe atom to Zr atoms.