Computer design of novel diamond-like crystals of fullerenes C₂₈ and C₄₀: Stability, crystal structure, and elastic and electronic properties

Novel dense crystalline modifications of small C n fullerenes (n = 28, 40), i.e., the so-called autointercalated hyperdiamonds with combined covalent and van der Waals types of C n -C n interatomic bonds, are proposed and simulated. The crystal structures of these modifications consist of C n fullerene molecules forming diamond lattices in which holes are occupied by the same fullerene molecules. The crystal structures, elastic and electronic properties, and energies of formation of the C n autointercalated hyperdiamonds are calculated using the density-functional-based tight-binding (DFTB) method. The bulk moduli of the autointercalated hyperdiamonds are found to increase abruptly as compared to those of the initial hyperdiamonds. It is established that the C28 and C40 autointercalated hyperdiamonds are semiconductors with the band gaps approximately equal to 1.30 and 0.94 eV, respectively.