Trends In Geometric And Properties Of Bimetallic Clusters Cu_nM (M=V,Nb;n=1-12): Insight From Density Functional Calculations

In this paper,a systematic quantum chemical investigation on the geometric,energetic,electronic and magnetic properties of bimetallic clusters CunM(n=1-12)is performed by using Density Functional Theory.The calculated results show that the structures of pure copper clusters are changed when V and Nb atoms doped.The structural evolution of CunV and CunNb clusters both favor a compact and icosahedral growth pattern and V and Nb atoms favor occupying the most highly coordinated positions.(1)The CunV(n=1-12)clusters are performed by using BPW91/LanL2 DZ calculations.The calculated results of average binding energies,embedding energies,and the second-order difference of energies show that the thermodynamic stabilities of the host clusters can be enhanced to some extent by doping V atom in pure copper clusters.Combined with the analyses on HOMO-LUMO energy gaps of CunV clusters,the atomic shape plays an important role in clusters stability.The electronic properties of CunV clusters are analyzed through the vertical ionization potential(VIP),vertical electron affinity(VEA)and chemical hardness(?).The VIPs of CunV clusters have no obvious change,which means the abilities of Cun V(n=1-12)clusters to lose an electron are basically same.While the VEAs tend to increase in the mass with the growth of the clusters,which means CunV(n=1-12)clusters are likely to get an electron and have large electronegativities.The chemical activities of CunV clusters system are be enhanced when V atom doped.The magnetism calculations show that when doping V atom in copper clusters,the cluster system generate a very large magnetic moment.When n=6-11,the magnetic moments decrease linearly.Because of the Jahn-Teller effect and the structure distortion,the degenerate orbitals split.The NBO population analyses show that there exits charge transfer in V atom and between Cu and V atoms.The electronic density of state shows that the magnetic moment contribution mainly comes from the 3d orbital of doping-V atom,while the Cu atoms contribute little.(2)The calculations are used by BPW91 methods.The 6-311+g(d)basis set is used for the copper atoms,and the cc-pvdz-pp basis set is used for the Nb atoms.The calculated results of average binding energies,embedding energies,and the second-order difference of energies show that the thermodynamic stability of the host clusters can be enhanced by doping Nb atom in pure copper clusters.The analyses of electronic properties of Cun V clusters show that the VEAs of CunV clusters tend to increase in the mass with the growth of the clusters,and the clusters tend to become anion clusters.The analyses of orbital energy levels for Cu12 V and Cu12 Nb clusters show that their valece electron configuration is 1S2,2P6,1D9.This configuration needs an electron to form 18 electronic stability strcture.The magnetism calculations show that when doping Nb atom in copper clusters,the cluster system generates a very large magnetic moment.The NBO population analyses show that there exits charge transfer in Nb atom and between Cu and Nb atoms.The electronic density of states show that the magnetic moment contribution mainly comes from the 4d orbital of doping-Nb atom.The analyses of infrare spectrum of CunNb(n=2-12)clusters show that the most strongest absorption peaks are found in f=200-300 cm-1.This phenomenon is caused by antisymmetric stretching vibration.When f=200-300 cm-1,the peaks are caused by symmetric stretching vibration or flexural vibration.The most active peaks of Raman spectrum are found in f=200-300 cm-1,which is caused by breathing vibration of all atoms.