Hole-Doping Suppresses Competing Magnetism in High-DOS C136 Carbon Schwarzite: A Computational Route Toward Superconductivity in Negative-Curvature Carbon Networks

Abstract

Carbon schwarzites are negative-curvature carbon networks with electronic structures distinct from graphene, fullerenes, and conventional carbon allotropes. Here we report a spin-polarized first-principles screening study of D-type C136 carbon schwarzite focused on the competition between magnetism, doping, and high-DOS metallic behavior. Neutral C136 has a robust competing magnetic branch, with total magnetization of about 11.01-11.03 Bohr magnetons per 136-atom cell. Charged-cell calculations reveal a clear electron-hole asymmetry: adding two electrons per cell increases the total magnetization to 12.11 Bohr magnetons per cell, while removing two electrons reduces it to 9.61. Further hole doping suppresses the magnetic branch monotonically, giving 8.02, 6.34, and 4.76 Bohr magnetons per cell for removal of 4, 6, and 8 electrons, respectively. The most strongly hole-doped point, h8, was examined with spin-polarized NSCF and density-of-states calculations on a 4x4x4 k-point mesh. The NSCF Fermi energy, -0.7414 eV, agrees with the SCF value, -0.7413 eV. The DOS remains high near the Fermi level: at E = -0.740 eV, the total DOS is about 44.69 states/eV/cell, with DOS_up = 33.11 and DOS_down = 11.58 states/eV/cell. Thus h8 combines substantial suppression of the competing magnetic branch with preservation of a high-DOS metallic state. We do not claim superconductivity in C136. Instead, these calculations identify hole doping as a route for suppressing a competing magnetic instability while preserving electronic conditions relevant for further superconductivity screening. Lattice stability, electron-phonon coupling, and transition-temperature estimates remain open problems.