Abstract
An oblate rhombohedral unit cell of α-boron crystal was constructed and the transition of two icosahedra lying at the ends of its short body diagonal was simulated. By applying ab initio Hartree-Fock self-consistent field methods different configurations of two icosahedra were investigated. The obtained structure B24 exhibits a closed tubular form of two coalesced interpenetrating icosahedra. A model based on a B21 cluster, composed of two icosahedra with mutual three interfacing atoms suggested in a previous study, was also investigated.