Electronic structure of the ${\mathrm{Ba}}_4{\mathrm{C}}_{60}$ superconductor

We study the electronic structure of the superconducting body-centered-orthorhombic fulleride ${\mathrm{Ba}}_4{\mathrm{C}}_{60}$ using the local-density approximation in the density-functional theory. It is found that Ba states are strongly hybridized with ${\mathrm{C}}_{60}$ states through pentagons, explaining the observed lattice-constant differences, $a>b>c.\mathrm{}$ Due to this hybridization and to a rather low symmetry of the lattice causing the splitting of states, the $t_{1g}$-derived conduction band partially occupied by two electrons is found to be relatively wide. Fermi surfaces also show noncubic nature and contain dual quasiplanar sheets parallel to the $a-b$ plane in the momentum space, giving rise to a quasinesting vector parallel to the c axis.