Superconductivity in the Li-B-C system at 100 GPa

Layer Li-B-C compounds have been shown to have feasible superconductivity. Using the adaptive genetic algorithm, we predict the structures of the Li-B-C system at 100 GPa. We identify several low-enthalpy metallic phases with stoichiometries of $\mathrm{Li}{\mathrm{B}}_{2}\mathrm{C}$, $\mathrm{Li}{\mathrm{B}}_{3}\mathrm{C}$, ${\mathrm{Li}}_{2}\mathrm{B}{\mathrm{C}}_{2}$, ${\mathrm{Li}}_{3}{\mathrm{B}}_{2}{\mathrm{C}}_{3}$, ${\mathrm{Li}}_{3}\mathrm{BC}$, and ${\mathrm{Li}}_{5}\mathrm{BC}$. Using a fast screening method of electron-phonon interaction, we find that $\mathrm{Li}{\mathrm{B}}_{3}\mathrm{C}$ is a promising candidate for superconductivity. The consecutive calculations using the full Brillouin zone confirm the existence of the strong electron-phonon coupling (EPC) in this system. The anharmonic B-C phonon modes near the zone center provide the major contribution to the EPC. The EPC constant is 1.40, and the estimated critical temperature is 22 K. In this paper, we indicate that superconductivity can also happen without a layered structural motif in the Li-B-C system. We also demonstrate an effective strategy for crystal structure prediction of superconducting materials.