Prediction of a Superhard Material: B4C4

Using a newly developed particle swarm optimization (PSO) algorithm for crystal structural prediction, we have explored the possible crystal structure of BC. A new P4(2)/mnm structure (B4C4) for BC was predicted. Then, its structure, elastic properties, electronic structure, and chemical bonding have been investigated by first-principles calculations with the density functional theory. The phonon calculation and elastic constants have confirmed that the predicted B4C4 is dynamically and mechanically stable, respectively. The analysis of the electron structure of the predicted B4C4 has indicated that it is an insulator, and high electron localization has been observed in the region among B-C and C-C atoms, indicating strong covalent B-C and C-C bonds.