Theoretical Studies On The Structures And Magnetic Properties Of Co_nAu,(CoAl)_n, And Co_nO Clusters

Over the last two decades, transition metal (TM) clusters haveattracted a lot of attention of the researchers in related field due totheir novel physical and chemical properties. A lot of theoretical andexperiment investigations for the TM clusters have improved thecomprehensive understanding on their structures, electronic andmagnetic properties. More recently, the bimetallic TM clusters haveattracted considerable attention in the last years, because thephysicochemistry properties of them can be tailored by varying boththe size and composition for a specific purpose. As a result, aiming attheir exotic physical and chemical properties, investigating theelectronic structure and magnetism of bimetallic TM alloy clustershas become one of the most active research subjects in the field ofcluster physics and Chemical.In this paper, we chose the cobalt-based bimetallic clusters whichare one of the most promising species in the filed of magneticmaterials and catalytic reaction. The structures, electronic andmagnetic properties of ConAu,(CoAl)n, and ConO clusters have beensystematically investigated by using density functional theory, and explored the correlation between geometrical, electronic, structuresand magnetic properties of the bimetallic TM alloy clusters. The maincontents and results are as follows:1. Structure, stability, and magnetism of ConAu (n=1-9) alloy clustersThe configurations, stabilities, electronic, and magnetic propertiesof ConAu (n=1-9) clusters have been systematically investigated byusing density functional theory. The growth way for ConAu (n=1,3-7)clusters is Au-substituted Con+1clusters. And the growth way forConAu (n=2,8,9) clusters is that the Au atom occupies a peripheralposition of Conclusters. The fragmentation energy and thesecond-order difference energy of the ground-state ConAu clustersshow a pronounced odd-even oscillation with the number of Co atoms,and the clusters exhibit higher stability at n=5. Compared withcorresponding pure Con+1clusters, the total magnetic moment isreduced by2μBfor most of ConAu clusters except n=3and8. Themagnetic moment contribution of Au atom is very small, and thedoping-Au atom almost has no effect on the average magneticmoment of Co atom which still keeps about2μBof magnetism of pureCon+1clusters, resulting in the decreasing magnetism of the doping-Aucobalt clusters.2. Structure, stability, and magnetism of (CoAl)n(n=1-6) alloy clustersBy using first-principles DFT-GGA calculations, we systematicallyinvestigate the structures, electronic and magnetic properties of(CoAl)nclusters. The (CoAl)nclusters exist a lot of low-lying isomerswith very close energy in the near ground state structure. The groundstate structures show the classic transition metal close packingstructure. In the (CoAl)nclusters, the covalent and ionic bonds compete with each other, covalent bonds weaken and ionic bondsprevailed, resulting that the HOMO-LUMO gap appear to a downwardtrend as the clusters size increase. The total magnetic moment ofthe ground state (CoAl)nclusters presents half a trapezoidal shapechange trend. This result is attributed to the magnetic coupling,charge transfer between the atoms of CoAl alloy clusters, and theimpact of non-magnetism Al element embeding on the spinpolarization of the cobalt atoms.3. Structure, stability, and magnetism of ConO (n=2-10) alloy clustersBased on DFT-GGA calculations, we systematically investigate thestructures, electronic and magnetic properties of ConO (n=2-10)clusters. The growth way for ConO clusters is that the O atomoccupies the surface-capped position on Con(n=2-10) clusters. Thesubstitution of Co atom in Concluster by a O atom improves thestability of the host cluster. Maximum peaks of second-order energydifferences are observed at n=3,6, and8, implying that these clusterspossess relatively higher stability than their respective neighbors.Compared with corresponding pure Conclusters, the doping clusterspossess higher HOMO-LUMO gaps, indicating their high chemicalinertness. In addition， the doped O atom exhibits the differentinfluence on the magnetism of alloy clusters. This is furtherinvestigated using the local magnetic moment and partial and localdensity of states analysis.