Family of low-energy elongated Si{sub {ital n}} ({ital n}{le}50) clusters

A family of stable elongated silicon clusters built from a simple stacking scheme has been discovered through local-density approximation (LDA) molecular-cluster calculations. These surprisingly well-bound structures were constructed by layering triangles of atoms with a common axis and adding one or two caps. For small clusters, one cap is significantly more stable than two, and for a few cases we have replaced the caps with other atoms (Be,B,N), which further increased the stability by closing the electronic shells. These clusters show distinct structural features for odd and even numbers of triangles, with a transition to greater stability for an odd number of triangles at {ital n}=29. For {ital n}=20 we used the quantum Monte Carlo method in order to assess the accuracy of LDA for the energy ordering of various isomers.