From van der Waals to metallic bonding: The growth of Be clusters

Ab initio molecular-dynamics simulations were used to predict structures for beryllium clusters of two to twenty atoms. As a function of cluster size (N) the sp hybridization converges quickly to the bulk value by N=6. Clusters with N>7 grow two dimensionally through a mechanism of prism addition and rhombus capping, beginning a growth pattern which quickly leads to an hcp lattice fragment. By N=15 the structure contains an element quantitatively similar to the primitive cell of the bulk. Despite strong directional bonding, the relative stability distribution obeys the predictions of the electronic shell model.