First-principles study on metal-doped icosahedralB12solids

Theoretical exploration of a group of ‘‘${\mathrm{C}}_{60}$-like’’ ${\mathrm{B}}_{12}$-based materials, ${\mathit{A}}_{\mathit{x}}$ ${\mathrm{B}}_{12}$, with A=(Li and Ca) and x=1–4, is made by performing local-density approximation Gaussian basis calculations of the total energy, heats of formation, lattice constant, electronic structure, density of states, and bulk modulus of the putative compounds, using ab initio pseudopotentials. Lithium-doped materials are mostly demonstrated to give sufficient heats of formation, whereas it is shown that all Ca-doped materials are unstable, including ${\mathrm{Li}}_2$ ${\mathrm{CaB}}_{12}$. Results are presented only for the stable and metastable ${\mathrm{Li}}_{\mathit{x}}$ ${\mathrm{B}}_{12}$ and compared with other current theoretical calculations on ${\mathrm{K}}_3$ ${\mathrm{C}}_{60}$. The possibility of superconductivity is also discussed. The band-structure calculations reveal essentially metallic behavior of ${\mathrm{Li}}_{\mathit{x}}$ ${\mathrm{B}}_{12}$. Important differences are found in the energy band structures, particularly in bands near the Fermi level, that would be reflected in superconductivity of these systems. Favorable superconducting properties are expected for ${\mathrm{Li}}_3$ ${\mathrm{B}}_{12}$, in the context of sufficiently high N(${\mathit{E}}_{\mathit{F}}$) and obtained bulk modulus that is indicative of strong electron-phonon coupling. © 1996 The American Physical Society.