Boron aggregation in the ground states of boron-carbon fullerenes

We present unexpected structural motifs for boron-carbon nanocages of the stoichiometries ${\mathrm{B}}_{12}{\mathrm{C}}_{48}$ and ${\mathrm{B}}_{12}{\mathrm{C}}_{50}$, based on first-principles calculations. These configurations are distinct from those proposed so far because the boron atoms are not isolated and distributed over the entire surface of the cages, but rather aggregate at one location to form a patch. Our putative ground state of ${\mathrm{B}}_{12}{\mathrm{C}}_{48}$ is 1.8 eV lower in energy than the previously proposed ground state and violates all the suggested empirical rules for constructing low-energy fullerenes. The ${\mathrm{B}}_{12}{\mathrm{C}}_{50}$ configuration is energetically even more favorable than ${\mathrm{B}}_{12}{\mathrm{C}}_{48}$, showing that structures derived from the ${\mathrm{C}}_{60}$ buckminsterfullerene are not necessarily magic sizes for heterofullerenes.

Figure 1

Plot of the 12 energetically most favorable structures, the most favorable one containing a filled heptagon and the three lowest diluted configurations for ${\mathrm{B}}_{12}{\mathrm{C}}_{48}$, together with the low-energy part of the spectrum. The coloring scheme is explained in the text.

Figure 2

The energy difference vs the RMSD, both with respect to the putative ground states.

Figure 3

The low-energy part of the spectrum for ${\mathrm{B}}_{12}{\mathrm{C}}_{50}$, together with figures of the 12 energetically lowest structures, the most favorable one containing a filled pentagon and the two most favorable diluted configurations.