First-principles study of the equilibrium structures of Si-n clusters

Abstract

We investigate the atomic structure of Si-n (n = 9-14) clusters using the first-principles pseudopotential method within the local-density-functional approximation (LDA). The equilibrium geometries of small clusters with n less than or equal to 12 tend to be capped prismatic structures. For n = 13, we find a surface-like metallic compact structure which is derived from a capped icosahedron and competes with a stable trigonal prism, while this structure is the most stable for n = 14. These results are compatible with the observed stability of Si-13 and Si-14, as compared to Si-n clusters with nearby Values of n, against chemical reactions with simple molecules. The effect of electron-electron correlations on the energetics of isomers with n = 13 is examined through variational quantum Monte Carlo calculations, and the LDA energy ordering remains unchanged, consistently with previous diffusion quantum Monte Carlo calculations.