Electronic structure, stability and non-linear optical properties of aza-fullerenes C60-2nN2n(n=1–12)

Abstract

Through ab initio based density functional theory calculations, we have investigated the electronic structure, stability and non-linear optical properties of a series of nitrogen substituted fullerenes (azafullerenes) with the general formula C60-2nN2n (n=1–12). For each system, we have considered different possible isomers and the minimum energy isomer is subjected to further detailed investigations. We have calculated different properties such as HOMO-LUMO gaps, vertical ionization potentials, vertical electron affinities, etc. to verify the stability of the considered fullerenes. From the Hessian calculations, it is observed that all the fullerenes are not only associated with real vibrational frequencies, but the minimum frequencies are also found to be considerably large which further confirms the stability of the considered fullerenes. We find that the presence of unperturbed C6 rings enhances the stability of the fullerene whereas, the -N-C-N- fragments are found to destabilize the structure. At lower doping concentration, the stabilization due to C6 is more predominant and as the doping concentration is increased, the destabilization due to nitrogen-nitrogen repulsion plays a more important role. Our calculated polarizability and hyperpolarizability parameters of C60 are found to be in good agreement with the earlier reported results. On nitrogen doping, considerable variation is observed in the non-linear optical coefficients, which can be helpful in designing new photonic devices.

Introduction and theoretical investigation of new azafullerene structures with nitrogen belts

“…The selected SN-isomers of both C 40 N 20 and C 42 N 18 molecules are the most stable isomers of these molecules reported by Srinivasu et al [34]. They studied these SN-isomers in 2012 using GAMESS software at B3LYP/6-31G [34].…”

“…Though, we think that weaker N-N link claimed by Srinivasu et al [34], (due to the N-N repulsion) should not be the reason to abandon research on the azafullerene structures with this type of connections. Also, according to our literature survey, several experimental works [36,37], and many theoretical investigations have been performed on the bonding and stability of polynitrogen molecules [38] and nitrogen clusters such as N 4 , N 8 , N 18 and N 20 [39][40][41][42].…”

“…They studied these SN-isomers in 2012 using GAMESS software at B3LYP/6-31G [34]. However, in the present study, for the first time, the SN-isomers have been studied using Gaussian program [46] by including polarization functions on all atoms, and also have been used for comparison with NB-isomers.…”

“…In the later study, it was showed that in the low concentrations of nitrogen, the stability is more due to all-carbon hexagonal rings (ACHRs), but in the higher concentrations of nitrogen, the N-N repulsions increase the relative energy [34].…”

“…In all subsequent studies performed on heterofullerenes with the form C 60-n N n , the nitrogen atoms were considered as not-adjacent to each other; for instance the structural studies of C 60-n N n (for n=1-12) by Sharma et al [33], and C 60-2n N 2n (for n=1-12) by Srinivasu et al [34]. In the later study, it was showed that in the low concentrations of nitrogen, the stability is more due to all-carbon hexagonal rings (ACHRs), but in the higher concentrations of nitrogen, the N-N repulsions increase the relative energy [34].…”