Characterization of titanium influences on structure and thermodynamic stability of novel C20-nTin nanofullerenes (n=1-5): a density functional perspective.

In this survey, effects of titanium heteroatom(s) on structural parameters and thermodynamic stability of C20 fullerene and its C20-nTin derivatives (n = 1-5) are compared and contrasted, at DFT levels of theory. The results show that in going from C19Ti1 to C15Ti5, binding energy increases while absolute value heat of atomization decreases. According to vibrational frequency analysis, excepting C16Ti4-1, the other optimized structures give no imaginary frequency as true minima. The calculated binding energy of 887.12 kcal mol-1/atom displays C15Ti5 as the most thermodynamically stable heterofullerene. It has Cs symmetry and contains five titanium atoms alternatively in equatorial position. The substitutional doping of C20 fullerene leads to high Mülliken charge distribution upon the surfaces of the resulted heterofullerenes especially C19Ti1 as suitable hydrogen storage. The contour plots indicate the most negative electrostatic potential by red color for C atoms, whereas the most positive electrostatic potential by yellow color for Ti heteroatoms. The contour plots and multiwfn analysis exhibit charge transfer from titanium heteroatoms to the neighboring carbon atoms. Furthermore, the resulted electron density maps from multiwfn qualitatively confirm the contour plot's findings. The hydrogen adsorption is an endothermic process for C20 fullerene and exothermic process for C20-nTin heterofullerenes. Major criteria examined for thermodynamic stability; from C19Ti1 to C15Ti5, binding energy and hydrogen adsorption increase while heat of atomization decreases.