Body-Centered OrthorhombicC16: A Novel Topological Node-Line Semimetal

We identify by ab initio calculations a novel topological semimetal carbon phase in all-$s{p}^{2}$ bonding networks with a 16-atom body-centered orthorhombic unit cell, termed bco-${\mathrm{C}}_{16}$. Total-energy calculations show that bco-${\mathrm{C}}_{16}$ is comparable to solid fcc-${\mathrm{C}}_{60}$ in energetic stability, and phonon and molecular dynamics simulations confirm its dynamical stability. This all-$s{p}^{2}$ carbon allotrope can be regarded as a three-dimensional modification of graphite, and its simulated x-ray diffraction (XRD) pattern matches well a previously unexplained diffraction peak in measured XRD spectra of detonation and chimney soot, indicating its presence in the specimen. Electronic band structure calculations reveal that bco-${\mathrm{C}}_{16}$ is a topological node-line semimetal with a single nodal ring. These findings establish a novel carbon phase with intriguing structural and electronic properties of fundamental significance and practical interest.