Three-dimensional three-connected tetragonal BN: Ab initio calculations

We identify by ab initio calculations of a three-dimensional three-connected chiral framework structure of BN (named cT8-BN) in I-42d (D2d12) symmetry, which has a body-centered tetragonal unit cell comprising 4-fold helical chains with complementary chirality. Our calculations show that the cT8-BN is a high ductile material with a small density of 2.43 g/cm3. The phonon and electronic band structures reveal that it is dynamic stable and shows as a transparent insulator with a large indirect band gap of 5.38 eV. These results broaden our understanding of the BN compounds.