DFT Investigation of structure, stability, NBO charge on Titanium—Nitrogen nanoheterofullerenes evolved from a small nanocage

In this DFT approach, we are performed geometrically and electronically properties of Ti—N nanoheterocages developed from C20 fullerene with the molecular formula of C20-2nTinNn (n = 1-8), at B3LYP/6-311++G**, M062X/6-311++G**, B3PW91/6-311++G**, and B3LYP/AUG-cc-pVTZ levels of theory. Based on the vibrational frequency analysis, except for C4Ti8N8 structure, others are real minima and none deform as segregated open cage. Substituted doping C20 to its C20-2nTinNn derivatives are caused different ΔEHOMO-LUMO values and conductivity, so that there is no uniformity between the ΔEHOMO-LUMO and n (number of substituting Ti―N units) and C18Ti1N1 is found as the best insulated nanoheterofullerene, while C12Ti4N4 is considered as the strongest conductive nanocage. The results show good reliability among polarizability, and ionization potential with n. Thermodynamic stability and aromaticity (NICS values at cages centers) decreases as n increases. As such, the strong ring current in C18Ti1N1 becomes weak in other nanostructures studied under work because the pπ electrons are slightly shifted from Ti to N (and C) atoms also portions of valence electrons keep on localized over the N (and C) nuclei. Accordingly, on account of lack of N—N bonds and dispersion of eight Ti—N bonds in the symmetrical positions of cage, the C4Ti8N8 species conserves the cage structure, showing the lowest dipole moment of 0.00 Debye and the lowest positive charge on Ti atoms (+0.526). Considering the least absolute value of hydrogen adsorption energy │−18.9 kcal/mol│ and the highest positive charge on titanium heteroatom of C18Ti1N1 (+1.269), it seems that C18Ti1N1 is the best candidate for hydrogen storage.