Predicting Three-Dimensional Icosahedron-Based Boron B-60

The icosahedron-based bulk boron structures have extremely chemical and structural complexity, and are usually semiconductors at ambient conditions. Here we predict bulk boron phases with a 60-atom orthorhombic unit cell from an ab initio evolutionary structure search, termed as B-60. The metastable structures can be either a conductor or a semimetal depending on their interstitial atomic positions. In particular, an orthorhombic structure with Pnma symmetry (Pnma-B-60), consisting of B-12 icosahedra and twisted interstitial two-atom wide boron ribbons, is identified to be a topological node-line semimetal with potential superior electronic transport. The band structure and simulated electron-diffraction pattern of Pnina-B-60 are in satisfactory agreement with the experimental data, suggesting that it may exist in the form of nanomaterials.