An ab initio study of niobium (n = 2--11) clusters: structure, stability and magnetism

The ground-state configurations of the Nb_n (n= 2--11) clusters are studied through the first-principles calculations. It is found that niobium clusters (n= 2--11) tend to form compact structures with low symmetry. The clusters with 4, 8 and 10 atoms are found to be magic and have relatively large highest occupied--lowest unoccupied molecular orbital (HOMO-LUMO) gaps. The Nb_n clusters possess low magnetic moments, which exhibit an odd-even oscillational character. The analyses of calculated electronic density and population of the lowest-energy niobium clusters for n= 2, 3, 5, 7, 9, 11 show that the total magnetic moments of Nb_n originate mainly from a few Nb atoms with longer spacings between them in most cases, while they are located on two Nb atoms for n= 2, 3, 5. The total magnetic moments come mainly from the 4d local moments but with the exception of the Nb₅ cluster.