Structural Stability of Boron Clusters with Octahedral and Tetrahedral Symmetries

The structural stability of cagelike boron clusters with octahedral and tetrahedral symmetries has been investigated by means of first-principles calculations. Twenty-eight cluster models, ranging from B-10 to B-66, were systematically constructed using regular and semiregular polyhedra as prototypes. The binding energies per atom were, on the whole, slightly lower than those of icosahedral clusters B-80 and B-100, which are supposed to be the most stable in the icosahedral group. The larger dusters did not always have higher binding energies. Isothermal molecular dynamics simulations were performed to determine the deformation temperatures at which clusters began to break or change their structures. We found eight clusters that had nonzero deformation temperatures, indicating that they are in metastable states. The octahedral cluster B-18 had the highest deformation temperature among these, similar to that of icosahedral B-80 and B-100. The analysis of the electronic structure B-18 showed that it attained this high stability owing to Jahn-Teller distortion.