Theoretical study of the electronic structure of fullerene-cubane cocrystals

We present a first-principles study of the electronic structure of fullerene-cubane cocrystals, using density-functional theory at the local-density approximation level. The band structure is calculated along high-symmetry lines and compared with that of the fcc fullerene. We also present a study of the effect of possible potassium doping. We find potassium doping to have a similar effect on the density of states in the fullerene-cubane as in the pure fullerene. Charge transfer between the components of the studied materials is also calculated by Bader charge analysis. The possibility of a very small charge transfer between the cubane and the fullerene in the undoped fullerene-cubane cocrystal is discussed.

Figure 1

(Color online) Depiction of the ${\text{C}}_{60}{\text{C}}_8{\text{H}}_8$ cocrystal. The large green orbs are the tetrahedral voids, which may be possible to fill with, e.g., alkali ions.

Figure 2

(Color online) Electronic band structures of the studied materials in the $T_h$ orientation with the Fermi levels shifted to 0 eV. The upper panel shows ${\text{C}}_{60}$ (solid red online) and ${\text{C}}_{60}{\text{C}}_8{\text{H}}_8$ (short dashed blue online); the lower panel shows ${\text{K}}_2{\text{C}}_{60}$ (solid red online), ${\text{K}}_2{\text{C}}_{60}{\text{C}}_8{\text{H}}_8$ (short dashed blue online), and ${\text{K}}_3{\text{C}}_{60}$ (long dashed green online).

Figure 3

(Color online) Electronic density of states of the studied materials with the Fermi levels shifted to 0 eV. The upper panel shows ${\text{C}}_{60}$ (solid red online) and ${\text{C}}_{60}{\text{C}}_8{\text{H}}_8$ (short dashed blue online); the lower panel shows ${\text{K}}_2{\text{C}}_{60}$ (solid red online), ${\text{K}}_2{\text{C}}_{60}{\text{C}}_8{\text{H}}_8$ (short dashed blue online), and ${\text{K}}_3{\text{C}}_{60}$ (long dashed green online).

Figure 4

(Color online) Electronic density of states for fcc ${\text{C}}_{60}$ (left side) and the ${\text{C}}_{60}{\text{C}}_8{\text{H}}_8$ cocrystal (right side) in five different orientations (see text) with the Fermi levels shifted to 0 eV. The upper panel corresponds to a width of 0.02 eV for the $\gamma$ linewidth of the electronic states, while the middle and lower panels correspond to 0.04 and 0.08 eV, respectively. The large electronic linewidth in the lower panel models the case of freely rotating ${\text{C}}_{60}$, resulting in a nearly identical density of states for the five orientations, thus evidencing that while orientation has an important effect on the band structures, orientational effects are averaged out in the density of states and can be safely neglected.