Structure, stability, and electronic properties of AIP 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 AlnPnC20-2n heterofullerenic derivatives where n = 1-10 are probed, at density functional theory (OFT). Vibrational frequency calculations show that exclusive of Al6P6C8 and Al10P8C2, other species are true minima. Exploring of the optimized structures demonstrates the shrinkage of C=C double bonds to compensate for the longer C-Al, C-P and Al-P single bonds. The calculated binding energy, HOMO-LUMO gap and nucleus independent chemical shift at the cage center (NICS (0)) of Al1P1C18 shows it the most stable structure. While substituting of 1, 2, 3, 4, 6, and 7 Al-P units enhances kinetic stability of the resulting heterofullerenes against electronic excitations via increasing their HOMO-LUMO gap, doping of 5, 8, 9, and 10 Al-P 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 Al6P6C8, 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 Al4P4C12. 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, Al1P1C18, Al2P2C16, and Al10P10 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 Al1P1C18 and Al5P5C10 (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, Al1P1C18 structure is expected to be stabilized to a greater extent than the other species, which has been confirmed by the thermodynamic and kinetic data. (C) 2018 Elsevier B.V. All rights reserved.