Structural And Magnetic Properties Of Rhodium Clusters
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Date
2017-05
Authors
Soon, Yee Yeen
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Nanocluster has been a system of interest for the past decades due to its peculiar
size-dependent properties as compared to its bulk counterparts. As far as 4d transition
elements are concerned, rhodium (Rh) cluster is one of the most-debated systems. Bulk
Rh is a paramagnetic material, but when it is reduced to atomic dimension, its structural
and magnetic properties vary with the cluster size. This project is aimed to perform
systematic study to investigate the unusual properties at the lowest energy state of
RhN clusters, where N is the number of atoms ranged from 2 to 23. To study large
Rh clusters, Rh26, Rh30 and Rh38 are also included in the study. The lowest-energy
configurations of the clusters were obtained by performing two-stage optimization. A
random configuration was first globally optimized using an unbiased search algorithm,
BHGA (empirical Gupta potential as energy calculator), followed by local optimization
via first-principles DFT calculations with spin-polarized LCAO formalism. The effect
of spin contamination was not considered in the calculations. By performing energetic
analysis, Rh clusters with even number of atoms are found to be relatively stable,
compared to those with odd number of atoms. Structural properties of the clusters
were studied from their geometrical aspects, such as average radial bond distance,
average nearest neighbour distance and molecular symmetry. Size-dependent magnetic
properties of the clusters were presented and related to their symmetries. Electronic
structures of Rh clusters were studied to further understand how are the electrons
distribute over the structures via population analysis. In general, the results from current
study agree with previous works. The new results obtained in this thesis include (i)
optimized configurations of larger clusters that are rarely reported previously such as
Rh26, Rh30 and Rh38, (ii) Rh clusters become weakly magnetic when the number of
atoms exceeds 19, and (iii) unexpected magnetic ordering in some clusters are revealed,
in which negative spins are found in selected atoms in these clusters.
Description
Keywords
Structural and magnetic properties , of rhodium clusters