Systematic ab initio investigation of bare boron clusters:mDetermination of the geometryand electronic structures of Bn (n=2–14)

Based on ab initio quantum-chemical methods, accurate calculations on small boron clusters ${\mathrm{B}}_{\mathrm{n}}$ (n=2--14) were carried out to determine their electronic and geometric structures. The geometry optimization with a linear search of local minima on the potential-energy surface was performed using analytical gradients in the framework of the restricted Hartree-Fock self-consistent-field approach. Most of the final structures of the boron clusters (n>9) are composed of two fundamental units:meither of hexagonal or of pentagonal pyramids. Proposing an 'Aufbau principle' one can easily construct various highly stable boron species. The resulting quasiplanar and convex structures can be considered as fragments of planar surfaces and as segments of nanotubes or hollow spheres, respectively.