Structural isomerism of niobium clusters and its role on reactivity

Structures and energetics of Nb clusters are studied using a many-body potential based on the tight binding formulation and molecular dynamics simulations. Local and global minima are searched using steepest descent and conjugate gradient methods. Sequences of minima are thus ordered by energy revealing energetically degenerate isomers. While Nbn clusters for n ≤ 7 do not exhibit any structural isomerism, larger Nbn clusters do. In particular, Nb11 has two isomers with almost the same binding energy but completely different geometries. The role of geometry on reactivity is discussed and compared with recent experiments.