First-principles prediction of superconductivity in MgB3C3

From first-principles density functional theory calculations, we propose hexagonal layered MgB3C3 as a potential phonon-mediated superconductor at 59 K, which is far higher than the superconductivity of MgB2 (approximate to 39 K). The MgB3C3 is energetically and dynamically stable at ambient pressure in the P-62m hexagonal structure with c/a approximate to 0.79 and forms in stacks of honeycomb B-C layers with Mg as a space filler. Band structure calculations indicate that the bands at the Fermi level derive mainly from B and C orbitals in which two sigma and two pi bands both contribute to the total density of state. The pi bands are found to be strongly coupled with out-of-plane acoustic phonon mode, while the sigma bands coupled with the in-plane bond-stretching optical E' phonon modes produces a sizable superconductivity in MgB3C3.