Structure, stability, and electronic properties of AlP nanocages evolved from the world's smallest caged fullerene C20: A computational study at DFT

5 years ago

Structure, stability, and electronic properties of AlP nanocages evolved from the world's smallest caged fullerene C20: A computational study at DFT

The stability, geometry, and electronic properties of C 20 and its Al n P n C 20-2n heterofullerenic derivatives where n = 1–10 are probed, at density functional theory (DFT). Vibrational frequency calculations show that exclusive of Al 6 P 6 C 8 and Al 10 P 8 C 2 , other species are true minima. Exploring of the optimized structures demonstrates the shrinkage of CC double bonds to compensate for the longer CAl, CP and AlP single bonds. The calculated binding energy, HOMO–LUMO gap and nucleus independent chemical shift at the cage center (NICS (0)) of Al 1 P 1 C 18 shows it the most stable structure. While substituting of 1, 2, 3, 4, 6, and 7 AlP units enhances kinetic stability of the resulting heterofullerenes against electronic excitations via increasing their HOMO–LUMO gap, doping of 5, 8, 9, and 10 AlP units increases the conductivity of heterofullerenes through decreasing their band gap. Substitutional doping leads to a high point charge upon the surfaces of all derivatives, especially the highest delocalization on Al 6 P 6 C 8 , with range of −2.056 to −1.261 charged carbons, +1.493 to +1.586 charged aluminums, and +0.513 to +0.801 charged phosphor atoms, followed by Al 4 P 4 C 12 . These high charge distributions on the surfaces of the studied analogous can develop their storage capacity and henceforth characterize them worthy of investigation for hydrogen storage. Also, Al 1 P 1 C 18 , Al 2 P 2 C 16 , and Al 10 P 10 are shown as the most aromatic and anti-aromatic nanocages with NICS (0) of −41.60, −39.82, and +22.59 ppm, respectively, compared to C 20 (−19.61 ppm). The computed higher dipole moment of Al 1 P 1 C 18 and Al 5 P 5 C 10 (4.06 and 3.29 Debye, respectively) exhibits higher reactivity potential and greater affinity of them to more polar solvents. Thus, in both gas phase and polar solvent, Al 1 P 1 C 18 structure is expected to be stabilized to a greater extent than the other species, which has been confirmed by the thermodynamic and kinetic data.

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DOI: S0022286018300358