Novel X- and Y-substituted heterofullerenes X4Y4C12 developed from the nanocage C20, where X = B, Al, Ga, Si and Y = N, P, As, Ge: a comparative investigation on their structural, stability, and electronic properties at DFT

DFT calculations are performed to compare and contrast C-20 -analogous heterofullerenes of the form X4Y4C12 , where X = B, Al, Ga, Si and Y = N, P, As, Ge, at B3LYP/AUG-cc-pVTZ. Substitution of C=C double bonds with the X-Y hetero bonds is an applicable strategy for obtaining highly doped stable heterofullerenes since it avoids weak X-X and Y-Y homo bonds. To be fabricated in the laboratory, heterofullerenes must be not only thermodynamically but also kinetically stable against electronic excitations. As a criterion of thermodynamical stability, the binding energy increases down a group of the periodic table. The calculated band gaps of 2.85 and 1.06 eV for B4N4C12 and Al4N4C12 , respectively, reveal them as the most and the least chemically stable heterofullerenes against electronic excitations. Al4N4C12 is predicted to have the lowest binding energy and the highest conductivity and charge transfer, making it the excellent candidate for hydrogen storage. The fill optimizations show that the hybrid cages undergo some distortions due to the substitution of the heteroatoms and the heterofullerenes with a bigger heteroatom (Al4N4C12 and Ga4N4C12 ) are more chemically reactive. We predict that B4N4C12 as the most thermodynamically and kinetically stable species has not only the largest heat of atomization but also the highest energy gap.