The principal differences between conventional tight-binding methods and a nonconventional tight-binding method proposed earlier by one of the authors ͓Z. M. Khakimov, Comput. Mater. Sci. 3, 95 ͑1994͔͒ are highlighted here. The latter has been optimized for simulation of the structure, cohesive energies, ionization potentials, and electronic affinities of silicon clusters. A single tight-binding approximation has been used to predict all of the above properties with accuracy comparable to state-of-the-art ab initio methods. This demonstrates the potential of tight-binding methods as a quantitative, predictive tool, provided they are based on an accurate total energy functional and exploit properly the individual properties of chemical elements, accounting for both intra-and interatomic charge redistributions.

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Silicon clusters with a diamond-like core and energetically competitive non-diamond clusters were comparatively studied using the nonconventional tight-binding molecular dynamics simulation method. Non-diamond clusters were constructed according to a quasi-onedimensional pentagon-based regular growth pattern. A non-trivial competition between surface and core reconstructions in the clusters, in order to reach energetically favorable atomic arrangements, was observed. This prevents unlimited growth via the one-dimensional pattern.Starting from Si 43 , there was substantial deviation from the stacked pentagon motif, and for Si 61 one end of these clusters became almost two-dimensional. The structure of clusters with a diamond-like core was subject to substantial reconstruction for the cluster sizes considered (≤ 71 atoms). By extrapolating the present results, a lower bound for the transition from non-diamond structure to diamond-like structure is estimated to be 115 atoms.